avcodec/exr: fix invalid shift in unpack_14()

Fixes: 6154/clusterfuzz-testcase-minimized-5762231061970944
Fixes: runtime error: shift exponent 63 is too large for 32-bit type 'int'

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpegSigned-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/exr.c

@@ -899,7 +899,7 @@ static int pxr24_uncompress(EXRContext *s, const uint8_t *src,
 
 static void unpack_14(const uint8_t b[14], uint16_t s[16])
 {
-    unsigned short shift = (b[ 2] >> 2);
+    unsigned short shift = (b[ 2] >> 2) & 15;
     unsigned short bias = (0x20 << shift);
     int i;