Fixed crash if initialization of EGL failed but was tried again later.

The internal function SDL_EGL_LoadLibrary() did not delete and remove a mostly
uninitialized data structure if loading the library first failed. A later try to
use EGL then skipped initialization and assumed it was previously successful
because the data structure now already existed. This led to at least one crash
in the internal function SDL_EGL_ChooseConfig() because a NULL pointer was
dereferenced to make a call to eglBindAPI().

visualtest/include/SDL_visualtest_mischelper.h

@@ -0,0 +1,26 @@
+/**
+ * \file mischelper.c 
+ *
+ * Header with miscellaneous helper functions.
+ */
+
+#ifndef _SDL_visualtest_mischelper_h
+#define _SDL_visualtest_mischelper_h
+
+/* Set up for C function definitions, even when using C++ */
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * Stores a 32 digit hexadecimal string representing the MD5 hash of the
+ * string \c str in \c hash.
+ */
+void SDLVisualTest_HashString(char* str, char hash[33]);
+
+/* Ends C function definitions when using C++ */
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* _SDL_visualtest_mischelper_h */