Fix gear rendering for Suppressor (#256)

Fix misaligned gear mask and a buffer overflow for cars which use more
than 8 gears, and thus pixelmaps other than HGEARS.PIX.

Signed-off-by: Artur Rojek <contact@artur-rojek.eu>

src/DETHRACE/common/displays.c

@@ -1160,15 +1160,26 @@ void DoInstruments(tU32 pThe_time) {
             } else {
                 gear = gCar_to_view->gear;
             }
+#if defined(DETHRACE_FIX_BUGS)
+/*
+ * The OG derives gear mask height of 28 by `gears_image->height / 8`, but
+ * this is only valid for HGEARS.PIX, which contains 8 gear images. Hardcoding
+ * this number fixes gear rendering for cars using HGEARS4.PIX, which consists
+ * of 11 gear images.
+ */
+#define GEAR_HEIGHT 28
+#else
+#define GEAR_HEIGHT ((int)gProgram_state.current_car.gears_image->height / 8)
+#endif
             DRPixelmapRectangleMaskedCopy(
                 gBack_screen,
                 the_wobble_x + gProgram_state.current_car.gear_x[gProgram_state.cockpit_on],
                 the_wobble_y + gProgram_state.current_car.gear_y[gProgram_state.cockpit_on],
                 gProgram_state.current_car.gears_image,
                 0,
-                (gear + 1) * ((int)gProgram_state.current_car.gears_image->height >> 3),
+                (gear + 1) * GEAR_HEIGHT,
                 gProgram_state.current_car.gears_image->width,
-                (int)gProgram_state.current_car.gears_image->height >> 3);
+                GEAR_HEIGHT);
         }
         speedo_image = gProgram_state.current_car.speedo_image[gProgram_state.cockpit_on];
         if (gProgram_state.current_car.speedo_radius_2[gProgram_state.cockpit_on] >= 0) {