softfloat: decrease MIN_EXP to cover full float range

floats are not necessarily normalized, so a normalized softfloat needs
MIN_EXP lowered by 23 to cover that range.

Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>
(cherry picked from commit 2d6f46d801)
Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>

libavutil/softfloat.h

@@ -27,7 +27,7 @@
 #include "avassert.h"
 #include "softfloat_tables.h"
 
-#define MIN_EXP -126
+#define MIN_EXP -149
 #define MAX_EXP  126
 #define ONE_BITS 29