libswcale: Fix possible string overflow in test.

In libswcale/tests/swcale.c, the function fileTest() calls sscanf in
an argument of "%12s" on character srcStr[] and dstStr[], which are
only 12 bytes.  So, if the input string is 12 characters, a
terminating null byte can be written past the end of these arrays.

This bug was found by cppcheck.
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit b8ed4930)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libswscale/swscale-test.c

@@ -297,10 +297,10 @@ static int fileTest(uint8_t *ref[4], int refStride[4], int w, int h, FILE *fp,
     while (fgets(buf, sizeof(buf), fp)) {
         struct Results r;
         enum AVPixelFormat srcFormat;
-        char srcStr[12];
+        char srcStr[13];
         int srcW = 0, srcH = 0;
         enum AVPixelFormat dstFormat;
-        char dstStr[12];
+        char dstStr[13];
         int dstW = 0, dstH = 0;
         int flags;
         int ret;