qtrle: add more checks against pixel_ptr being negative.

CC:libav-stable@libav.org

libavcodec/qtrle.c

@@ -117,6 +117,7 @@ static inline void qtrle_decode_2n4bpp(QtrleContext *s, int row_ptr,
 
     while (lines_to_change--) {
         pixel_ptr = row_ptr + (num_pixels * (bytestream2_get_byte(&s->g) - 1));
+        CHECK_PIXEL_PTR(0);
 
         while ((rle_code = (signed char)bytestream2_get_byte(&s->g)) != -1) {
             if (rle_code == 0) {
@@ -171,6 +172,7 @@ static void qtrle_decode_8bpp(QtrleContext *s, int row_ptr, int lines_to_change)
 
     while (lines_to_change--) {
         pixel_ptr = row_ptr + (4 * (bytestream2_get_byte(&s->g) - 1));
+        CHECK_PIXEL_PTR(0);
 
         while ((rle_code = (signed char)bytestream2_get_byte(&s->g)) != -1) {
             if (rle_code == 0) {
@@ -220,6 +222,7 @@ static void qtrle_decode_16bpp(QtrleContext *s, int row_ptr, int lines_to_change
 
     while (lines_to_change--) {
         pixel_ptr = row_ptr + (bytestream2_get_byte(&s->g) - 1) * 2;
+        CHECK_PIXEL_PTR(0);
 
         while ((rle_code = (signed char)bytestream2_get_byte(&s->g)) != -1) {
             if (rle_code == 0) {
@@ -263,6 +266,7 @@ static void qtrle_decode_24bpp(QtrleContext *s, int row_ptr, int lines_to_change
 
     while (lines_to_change--) {
         pixel_ptr = row_ptr + (bytestream2_get_byte(&s->g) - 1) * 3;
+        CHECK_PIXEL_PTR(0);
 
         while ((rle_code = (signed char)bytestream2_get_byte(&s->g)) != -1) {
             if (rle_code == 0) {
@@ -309,6 +313,7 @@ static void qtrle_decode_32bpp(QtrleContext *s, int row_ptr, int lines_to_change
 
     while (lines_to_change--) {
         pixel_ptr = row_ptr + (bytestream2_get_byte(&s->g) - 1) * 4;
+        CHECK_PIXEL_PTR(0);
 
         while ((rle_code = (signed char)bytestream2_get_byte(&s->g)) != -1) {
             if (rle_code == 0) {