atimach64gx: Don't allow pitch to be zero.

Author: Wack0

devices/video/atimach64gx.cpp

@@ -703,8 +703,13 @@ void AtiMach64Gx::crtc_update()
 
     static uint8_t bits_per_pixel[8] = {0, 0, 4, 8, 16, 24, 32, 0};
 
-    int new_fb_pitch = extract_bits<uint32_t>(this->regs[ATI_CRTC_OFF_PITCH],
-        ATI_CRTC_PITCH, ATI_CRTC_PITCH_size) * bits_per_pixel[this->pixel_format];
+    int new_fb_pitch_reg = extract_bits<uint32_t>(this->regs[ATI_CRTC_OFF_PITCH],
+        ATI_CRTC_PITCH, ATI_CRTC_PITCH_size);
+    // HACK: should not be zero!
+    if (new_fb_pitch_reg == 0) {
+        new_fb_pitch_reg = active_width / 8; // "Display pitch in pixels * 8"
+    }
+    int new_fb_pitch = new_fb_pitch_reg * bits_per_pixel[this->pixel_format];
     if (new_fb_pitch != this->fb_pitch) {
         this->fb_pitch = new_fb_pitch;
         need_recalc = true;