Fix a crash on Android with Align2Npot2 (#8070)

* Fix a crash on Android with Align2Npot2

glGetString can be NULL. If stored in a string it triggers a SIGSEGV.
Instead do a basic strstr and verify the pointer
* Better Align2Npot2 check (+ performance)

src/client/tile.cpp

@@ -1012,13 +1012,14 @@ video::IImage * Align2Npot2(video::IImage * image,

	core::dimension2d<u32> dim = image->getDimension();

	std::string extensions = (char*) glGetString(GL_EXTENSIONS);

	// Only GLES2 is trusted to correctly report npot support
	if (get_GL_major_version() > 1 &&
			extensions.find("GL_OES_texture_npot") != std::string::npos) {
	// Note: we cache the boolean result. GL context will never change on Android.
	static const bool hasNPotSupport = get_GL_major_version() > 1 &&
		glGetString(GL_EXTENSIONS) && 
		strstr(glGetString(GL_EXTENSIONS), "GL_OES_texture_npot");

	if (hasNPotSupport)
		return image;
	}

	unsigned int height = npot2(dim.Height);
	unsigned int width  = npot2(dim.Width);