Fixed compile warnings about uninitialized variables in test library. Found by buildbot.
diff --git a/src/test/SDL_test_compare.c b/src/test/SDL_test_compare.c
index 45eb3c6..d06ead9 100644
--- a/src/test/SDL_test_compare.c
+++ b/src/test/SDL_test_compare.c
@@ -43,7 +43,7 @@ int SDLTest_CompareSurfaces(SDL_Surface *surface, SDL_Surface *referenceSurface,
int bpp, bpp_reference;
Uint8 *p, *p_reference;
int dist;
- int sampleErrorX, sampleErrorY, sampleDist;
+ int sampleErrorX = 0, sampleErrorY = 0, sampleDist = 0;
Uint8 R, G, B, A;
Uint8 Rd, Gd, Bd, Ad;
char imageFilename[128];