libavcodec/exr : fix float to uint16 conversion for negative float value

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit e46d6374)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/exr.c

@@ -216,9 +216,9 @@ static union av_intfloat32 exr_half2float(uint16_t hf)
  *
  * @return normalized 16-bit unsigned int
  */
-static inline uint16_t exr_flt2uint(uint32_t v)
+static inline uint16_t exr_flt2uint(int32_t v)
 {
-    unsigned int exp = v >> 23;
+    int32_t exp = v >> 23;
     // "HACK": negative values result in exp<  0, so clipping them to 0
     // is also handled by this condition, avoids explicit check for sign bit.
     if (exp <= 127 + 7 - 24) // we would shift out all bits anyway