chore: Clean up the spurious uses of sizeof(png_byte); fix the manual

By definition, `sizeof(png_byte)` is 1.

Remove all the occurences of `sizeof(png_byte)` from the code, and fix
a related typo in the libpng manual.

Also update the main .editorconfig file to reflect the fixing expected
by a FIXME note.

.editorconfig

@@ -16,8 +16,7 @@ indent_style = space
 [*.[chS]]
 indent_style = space
 max_doc_length = 80
-max_line_length = 81
-# FIXME: max_line_length should be 80
+max_line_length = 80
 
 [*.dfa]
 indent_style = space

libpng-manual.txt

@@ -1178,11 +1178,11 @@ where row_pointers is an array of pointers to the pixel data for each row:
 If you know your image size and pixel size ahead of time, you can allocate
 row_pointers prior to calling png_read_png() with
 
-   if (height > PNG_UINT_32_MAX/(sizeof (png_byte)))
+   if (height > PNG_UINT_32_MAX / (sizeof (png_bytep)))
       png_error(png_ptr,
           "Image is too tall to process in memory");
 
-   if (width > PNG_UINT_32_MAX/pixel_size)
+   if (width > PNG_UINT_32_MAX / pixel_size)
       png_error(png_ptr,
           "Image is too wide to process in memory");
 

libpng.3

@@ -1697,11 +1697,11 @@ where row_pointers is an array of pointers to the pixel data for each row:
 If you know your image size and pixel size ahead of time, you can allocate
 row_pointers prior to calling png_read_png() with
 
-   if (height > PNG_UINT_32_MAX/(sizeof (png_byte)))
+   if (height > PNG_UINT_32_MAX / (sizeof (png_bytep)))
       png_error(png_ptr,
           "Image is too tall to process in memory");
 
-   if (width > PNG_UINT_32_MAX/pixel_size)
+   if (width > PNG_UINT_32_MAX / pixel_size)
       png_error(png_ptr,
           "Image is too wide to process in memory");
 

pngrtran.c

@@ -440,7 +440,7 @@ png_set_quantize(png_structrp png_ptr, png_colorp palette,
       int i;
 
       png_ptr->quantize_index = (png_bytep)png_malloc(png_ptr,
-          (png_alloc_size_t)((png_uint_32)num_palette * (sizeof (png_byte))));
+          (png_alloc_size_t)num_palette);
       for (i = 0; i < num_palette; i++)
          png_ptr->quantize_index[i] = (png_byte)i;
    }
@@ -457,7 +457,7 @@ png_set_quantize(png_structrp png_ptr, png_colorp palette,
 
          /* Initialize an array to sort colors */
          png_ptr->quantize_sort = (png_bytep)png_malloc(png_ptr,
-             (png_alloc_size_t)((png_uint_32)num_palette * (sizeof (png_byte))));
+             (png_alloc_size_t)num_palette);
 
          /* Initialize the quantize_sort array */
          for (i = 0; i < num_palette; i++)
@@ -591,11 +591,9 @@ png_set_quantize(png_structrp png_ptr, png_colorp palette,
 
          /* Initialize palette index arrays */
          png_ptr->index_to_palette = (png_bytep)png_malloc(png_ptr,
-             (png_alloc_size_t)((png_uint_32)num_palette *
-             (sizeof (png_byte))));
+             (png_alloc_size_t)num_palette);
          png_ptr->palette_to_index = (png_bytep)png_malloc(png_ptr,
-             (png_alloc_size_t)((png_uint_32)num_palette *
-             (sizeof (png_byte))));
+             (png_alloc_size_t)num_palette);
 
          /* Initialize the sort array */
          for (i = 0; i < num_palette; i++)
@@ -760,12 +758,11 @@ png_set_quantize(png_structrp png_ptr, png_colorp palette,
       size_t num_entries = ((size_t)1 << total_bits);
 
       png_ptr->palette_lookup = (png_bytep)png_calloc(png_ptr,
-          (png_alloc_size_t)(num_entries * (sizeof (png_byte))));
+          (png_alloc_size_t)(num_entries));
 
-      distance = (png_bytep)png_malloc(png_ptr, (png_alloc_size_t)(num_entries *
-          (sizeof (png_byte))));
+      distance = (png_bytep)png_malloc(png_ptr, (png_alloc_size_t)num_entries);
 
-      memset(distance, 0xff, num_entries * (sizeof (png_byte)));
+      memset(distance, 0xff, num_entries);
 
       for (i = 0; i < num_palette; i++)
       {