Add another check to getProcessorSpeedMHz to prevent crashes on Unix when it's called with 0 parameter.

git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@5535 dfc29bdd-3216-0410-991c-e03cc46cb475

source/Irrlicht/COSOperator.cpp

@@ -200,7 +200,7 @@ bool COSOperator::getProcessorSpeedMHz(u32* MHz) const
 		}
 		fclose(file);
 	}
-	return (*MHz != 0);
+	return (MHz && *MHz != 0);
 #endif
 }