swscale/swscale: Do not crash on floats

Fixes: shift exponent 32 is too large for 32-bit type 'unsigned int'
Fixes: division by zero
Fixes: 391981061/clusterfuzz-testcase-minimized-ffmpeg_SWS_fuzzer-6691017763389440
Fixes: 392929028/clusterfuzz-testcase-minimized-ffmpeg_SWS_fuzzer-5142088307507200

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <[email protected]>

Author: michaelni

libswscale/swscale.c

@@ -623,7 +623,7 @@ av_cold void ff_sws_init_range_convert(SwsInternal *c)
 {
     c->lumConvertRange = NULL;
     c->chrConvertRange = NULL;
-    if (c->opts.src_range != c->opts.dst_range && !isAnyRGB(c->opts.dst_format)) {
+    if (c->opts.src_range != c->opts.dst_range && !isAnyRGB(c->opts.dst_format) && c->dstBpc < 32) {
         init_range_convert_constants(c);
         if (c->dstBpc <= 14) {
             if (c->opts.src_range) {