avutil/intfloat_readwrite: include common.h for isinf()

Solution based on rational.c, which uses isinf() too

This should fix compilation with msvc
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavutil/intfloat_readwrite.c

@@ -26,6 +26,7 @@
  */
 
 #include <stdint.h>
+#include "common.h"
 #include "mathematics.h"
 #include "intfloat_readwrite.h"