fix: only iterate the main executable program headers

The resource gets injected in the main executable, so there is no need
to iterate the other shared libraries that are loaded by the program.
This also resolves a security concern.

Refs: #77 (review)
Signed-off-by: Darshan Sen <raisinten@gmail.com>

postject-api.h

@@ -91,8 +91,9 @@ static int postject__dl_iterate_phdr_callback(struct dl_phdr_info* info,
     }
   }
 
-  // skip to the next shared object
-  return 0;
+  // wasn't able to find the note in the main executable program headers, so
+  // terminate the search
+  return 1;
 }
 #endif