Suppress -Wmaybe-uninitialized in tlistbox::place()

src/gui/widgets/listbox.cpp

@@ -313,6 +313,14 @@ bool tlistbox::update_content_size()
 	return false;
 }
 
+/* Suppress -Wmaybe-uninitialized warnings. @GregoryLundberg reported in IRC that GCC 6.2.1 with SCons gives a warning that
+ * the value of horizontal_scrollbar_position can be used uninitialized. It's of course not possible (boost::optional
+ * conversion to bool returns true only if the value is set), but GCC can't prove that to itself. */
+#ifdef __GNUC__
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
+#endif
+
 void tlistbox::place(const tpoint& origin, const tpoint& size)
 {
 	boost::optional<unsigned> vertical_scrollbar_position, horizontal_scrollbar_position;
@@ -346,6 +354,10 @@ void tlistbox::place(const tpoint& origin, const tpoint& size)
 	}
 }
 
+#ifdef __GNUC__
+#pragma GCC diagnostic pop
+#endif
+
 void tlistbox::resize_content(const int width_modification,
 							  const int height_modification,
 							  const int width_modification_pos,