testautomation_surface: Make sure error is set by the function we expect

If the error behaviour in one of these cases was wrong, that could have
been hidden by the error indicator remaining set from a previous test.

Signed-off-by: Simon McVittie <smcv@collabora.com>

test/testautomation_surface.c

@@ -765,6 +765,7 @@ int surface_testOverflow(void *arg)
                         "Expected \"%s\", got \"%s\"", expectedError, SDL_GetError());
 
     if (sizeof(size_t) == 4 && sizeof(int) >= 4) {
+        SDL_ClearError();
         expectedError = "Out of memory";
         /* 0x5555'5555 * 3bpp = 0xffff'ffff which fits in size_t, but adding
          * alignment padding makes it overflow */
@@ -772,15 +773,18 @@ int surface_testOverflow(void *arg)
         SDLTest_AssertCheck(surface == NULL, "Should detect overflow in width + alignment");
         SDLTest_AssertCheck(SDL_strcmp(SDL_GetError(), expectedError) == 0,
                             "Expected \"%s\", got \"%s\"", expectedError, SDL_GetError());
+        SDL_ClearError();
         /* 0x4000'0000 * 4bpp = 0x1'0000'0000 which (just) overflows */
         surface = SDL_CreateRGBSurfaceWithFormat(0, 0x40000000, 1, 32, SDL_PIXELFORMAT_ARGB8888);
         SDLTest_AssertCheck(surface == NULL, "Should detect overflow in width * bytes per pixel");
         SDLTest_AssertCheck(SDL_strcmp(SDL_GetError(), expectedError) == 0,
                             "Expected \"%s\", got \"%s\"", expectedError, SDL_GetError());
+        SDL_ClearError();
         surface = SDL_CreateRGBSurfaceWithFormat(0, (1 << 29) - 1, (1 << 29) - 1, 8, SDL_PIXELFORMAT_INDEX8);
         SDLTest_AssertCheck(surface == NULL, "Should detect overflow in width * height");
         SDLTest_AssertCheck(SDL_strcmp(SDL_GetError(), expectedError) == 0,
                             "Expected \"%s\", got \"%s\"", expectedError, SDL_GetError());
+        SDL_ClearError();
         surface = SDL_CreateRGBSurfaceWithFormat(0, (1 << 15) + 1, (1 << 15) + 1, 32, SDL_PIXELFORMAT_ARGB8888);
         SDLTest_AssertCheck(surface == NULL, "Should detect overflow in width * height * bytes per pixel");
         SDLTest_AssertCheck(SDL_strcmp(SDL_GetError(), expectedError) == 0,