Fixed comparison warning

Author: radarhere

src/libImaging/FliDecode.c

@@ -49,7 +49,7 @@ ImagingFliDecode(Imaging im, ImagingCodecState state, UINT8 *buf, Py_ssize_t byt
 
     framesize = I32(ptr);
     // there can be one pad byte in the framesize
-    if (bytes + (bytes % 2) < framesize) {
+    if ((unsigned)(bytes + (bytes % 2)) < framesize) {
         return 0;
     }
 
@@ -259,7 +259,7 @@ ImagingFliDecode(Imaging im, ImagingCodecState state, UINT8 *buf, Py_ssize_t byt
             state->errcode = IMAGING_CODEC_BROKEN;
             return -1;
         }
-        if (advance < 0 || advance > bytes) {
+        if (advance < 0 || advance > (unsigned)bytes) {
             state->errcode = IMAGING_CODEC_OVERRUN;
             return -1;
         }