libmp4v2: fix gcc7 build

srcpkgs/libmp4v2/patches/gcc7-fix-char_ptr.patch

@@ -0,0 +1,11 @@
+--- src/rtphint.cpp	2012-05-21 00:11:53.000000000 +0200
++++ src/rtphint.cpp	2017-05-20 19:33:12.524731466 +0200
+@@ -339,7 +339,7 @@
+                 pSlash = strchr(pSlash, '/');
+                 if (pSlash != NULL) {
+                     pSlash++;
+-                    if (pSlash != '\0') {
++                    if (*pSlash != '\0') {
+                         length = (uint32_t)strlen(pRtpMap) - (pSlash - pRtpMap);
+                         *ppEncodingParams = (char *)MP4Calloc(length + 1);
+                         strncpy(*ppEncodingParams, pSlash, length);