font: Fix double resource leak in font::pango_text

The impacted code path is only executed as part of the implementation of
the characters_per_line constraint.

According to the Pango documentation, PangoFontMetrics should be
released using pango_font_metrics_unref(), and PangoFont should be
released using *something* not specified. Existing code, and the
documentation for pango_fontset_get_font(), suggests the answer for the
latter is g_object_unref().

changelog.md

@@ -21,6 +21,7 @@
  ### User interface
    * Improved the Load dialog when there are no saved games for the current version, and also when there are corrupted files.
    * Re-added the pop-up when there are no saved games at all (issue #5517).
+   * Fixed resource leak in the Pango text rendering pipeline when using the characters_per_line constraint.
  ### WML Engine
    * Standard Location Filters now support gives_income=yes|no to make it simpler to match villages regardless of owner
  ### Miscellaneous and Bug Fixes

src/font/text.cpp

@@ -518,6 +518,9 @@ PangoRectangle pango_text::calculate_size(PangoLayout& layout) const
 		w *= characters_per_line_;
 
 		maximum_width = ceil(pango_units_to_double(w));
+
+		pango_font_metrics_unref(m);
+		g_object_unref(f);
 	} else {
 		maximum_width = maximum_width_;
 	}