Pointer arithmetic on void pointers is illegal

We quick-fix this by casting to char*; it might be more appropriate to
use char pointers in the first place.

ext/exif/exif.c

@@ -2148,9 +2148,9 @@ static void exif_iif_add_value(image_info_type *image_info, int section_index, c
 			} else {
 				info_value = &info_data->value;
 			}
-			vptr_end = value+value_len;
+			vptr_end = (char *) value + value_len;
 			for (idex=0,vptr=value; idex<(size_t)length; idex++,vptr=(char *) vptr + php_tiff_bytes_per_format[format]) {
-				if (vptr_end - vptr < php_tiff_bytes_per_format[format]) {
+				if ((char *) vptr_end - (char *) vptr < php_tiff_bytes_per_format[format]) {
 					exif_error_docref("exif_iif_add_value" EXIFERR_CC, image_info, E_WARNING, "Value too short");
 					break;
 				}