Lots of trivial tweaks to minimize compiler warnings, especially on 64-bit platform: Added missing type casts, changed types, added missing NULL checks.

libs/spandsp/src/image_translate.c

@@ -685,7 +685,6 @@ static int image_format_to_bytes_per_pixel(int image_format)
     case T4_IMAGE_TYPE_4COLOUR_12BIT:
         return 8;
     }
-    return 1;
 }
 /*- End of function --------------------------------------------------------*/