Fix typo: "Why" -> "What"

docs/manual/en/introduction/How-to-dispose-of-objects.html

@@ -98,7 +98,7 @@
 		nothing happens. No resources were allocated so there is also no need for clean up.
 	</p>
 
-	<h3>Why happens when you call *dispose()* on a texture but the image is not loaded yet?</h3>
+	<h3>What happens when you call *dispose()* on a texture but the image is not loaded yet?</h3>
 
 	<p>
 		Internal resources for a texture are only allocated if the image has fully loaded. If you dispose a texture before the image was loaded,