Ignore bmp reserved area (#1343)

The 4 bytes starting from the 0x06 offset of a bmp file are marked as
'Reserved' but it doesn't guarantee that these bytes are zeroed, some
applications uses this area for its own purposes and the output file
still a valid bmp file.

dlib/image_loader/image_loader.h

@@ -41,7 +41,6 @@ namespace dlib
             unsigned long bytes_read_so_far = 0;
             unsigned long bfSize;
             unsigned long bfOffBits;
-            unsigned long bfReserved;
             unsigned long biSize;
             unsigned long biWidth;
             int32 biHeight;
@@ -79,20 +78,12 @@ namespace dlib
             a = buf[i]; b = buf[i+1]; c = buf[i+2]; d = buf[i+3];
             bfSize = a | (b<<8) | (c<<16) | (d<<24);
 
-            i = 4;
-            a = buf[i]; b = buf[i+1]; c = buf[i+2]; d = buf[i+3];
-            bfReserved = a | (b<<8) | (c<<16) | (d<<24);
+            // Ignore the next 4 bytes (Reserved Area)
 
             i = 8;
             a = buf[i]; b = buf[i+1]; c = buf[i+2]; d = buf[i+3];
             bfOffBits = a | (b<<8) | (c<<16) | (d<<24);
 
-            // if this value isn't zero then there is something wrong
-            // with this bitmap.
-            if (bfReserved != 0)
-                throw image_load_error("bmp load error 4: reserved area not zero");
-
-
             // load the BITMAPINFOHEADER
             if (in.sgetn(reinterpret_cast<char*>(buf),40) != 40)
                 throw image_load_error("bmp load error 5: file too short");