Assert code's stdio interface was reading from the wrong variable.

Thanks to Frank Zago for the catch.

src/SDL_assert.c

@@ -337,16 +337,16 @@ SDL_PromptAssertion(const SDL_assert_data *data, void *userdata)
         if (SDL_strcmp(buf, "a") == 0) {
             state = SDL_ASSERTION_ABORT;
             break;
-        } else if (SDL_strcmp(envr, "b") == 0) {
+        } else if (SDL_strcmp(buf, "b") == 0) {
             state = SDL_ASSERTION_BREAK;
             break;
-        } else if (SDL_strcmp(envr, "r") == 0) {
+        } else if (SDL_strcmp(buf, "r") == 0) {
             state = SDL_ASSERTION_RETRY;
             break;
-        } else if (SDL_strcmp(envr, "i") == 0) {
+        } else if (SDL_strcmp(buf, "i") == 0) {
             state = SDL_ASSERTION_IGNORE;
             break;
-        } else if (SDL_strcmp(envr, "A") == 0) {
+        } else if (SDL_strcmp(buf, "A") == 0) {
             state = SDL_ASSERTION_ALWAYS_IGNORE;
             break;
         }