BMP loader fails to import images

[Calinou]

Godot version: Git 22c843b

OS/device including version: Fedora 30, GIMP 2.10.12, ImageMagick 6.9.10 (used for BMP conversion)

Issue description: The BMP loader fails to load images saved from GIMP and ImageMagick:

Unsupported bmp file: res://icon_from_gimp_16bit.bmp
core/io/image_loader.cpp:69 - Error loading image: res://icon_from_gimp_16bit.bmp
editor/editor_file_system.cpp:1786 - Error importing: res://icon_from_gimp_16bit.bmp
modules/bmp/image_loader_bmp.cpp:261 - Condition ' color_table_size == 0 ' is true. returned: ERR_BUG
core/io/image_loader.cpp:69 - Error loading image: res://icon_from_gimp_24bit.bmp
editor/editor_file_system.cpp:1786 - Error importing: res://icon_from_gimp_24bit.bmp
Unsupported bmp file: res://icon_from_gimp_32bit.bmp
core/io/image_loader.cpp:69 - Error loading image: res://icon_from_gimp_32bit.bmp
editor/editor_file_system.cpp:1786 - Error importing: res://icon_from_gimp_32bit.bmp
Unsupported bmp file: res://icon_from_imagemagick.bmp
core/io/image_loader.cpp:69 - Error loading image: res://icon_from_imagemagick.bmp
editor/editor_file_system.cpp:1786 - Error importing: res://icon_from_imagemagick.bmp

The exact file formats as described by the file command are:

icon_from_gimp_16bit.bmp:  PC bitmap, Windows 98/2000 and newer format, 64 x 64 x 16
icon_from_gimp_24bit.bmp:  PC bitmap, Windows 95/NT4 and newer format, 64 x 64 x 24
icon_from_gimp_32bit.bmp:  PC bitmap, Windows 98/2000 and newer format, 64 x 64 x 32
icon_from_imagemagick.bmp: PC bitmap, Windows 98/2000 and newer format, 64 x 64 x 32

Steps to reproduce: Load a BMP file and try to use it as a Sprite texture.

Minimal reproduction project: test_image_formats.zip

[Xrayez]

Managed to fix importing icon_from_gimp_24bit.bmp in linked PR, for other types it seems like the loader is complaining about not supported compression type:

godot/modules/bmp/image_loader_bmp.cpp

Lines 241 to 246 in 4e5310c

	// Compressed bitmaps not supported, stop parsing
	if (bmp_header.bmp_info_header.bmp_compression != BI_RGB) {
	ERR_EXPLAIN("Unsupported bmp file: " + f->get_path());
	f->close();
	ERR_FAIL_V(ERR_UNAVAILABLE);
	}

Even if these get resolved, 16-bit is also not supported by the loader.