Avoid querying buffer params for invalid buffers

Apps are free to enable attribute arrays and then dump the state before
binding a buffer via vertexAttribPointer. The state dumping code should
recognize this and avoid calling glGetBufferParameter since passing 0
(an invalid buffer) is an error.

Change-Id: Id3434b914281e9bd9d7157554ab6ef59558e292f
Reviewed-by: Pasi Keränen <pasi.keranen@digia.com>

src/canvasglstatedump.cpp

@@ -97,6 +97,9 @@ CanvasGLStateDump::~CanvasGLStateDump()
  */
 QString CanvasGLStateDump::getGLArrayObjectDump(int target, int arrayObject, int type)
 {
+    if (!arrayObject)
+        return "no buffer bound";
+
     QString stateDumpStr;
     glBindBuffer(target, arrayObject);