postproc/postprocess: Use size_t to hold strlen()s value

This should make no difference but its more correct
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libpostproc/postprocess.c

@@ -737,7 +737,7 @@ pp_mode *pp_get_mode_by_name_and_quality(const char *name, int quality)
         /* replace stuff from the replace Table */
         for(i=0; replaceTable[2*i]; i++){
             if(!strcmp(replaceTable[2*i], filterName)){
-                int newlen= strlen(replaceTable[2*i + 1]);
+                size_t newlen = strlen(replaceTable[2*i + 1]);
                 int plen;
                 int spaceLeft;