Use pango_font_metrics_get_height() to calculate font height

With newer versions of Pango and some fonts, the bottom of the
text is clipped (making underscores invisible). Use the correct
calculation when needed to avoid this.

Based on an original fix by Jeff Teunissen.

Closes hexchat#2449.

src/fe-gtk/xtext.c

@@ -283,8 +283,21 @@ backend_font_open (GtkXText *xtext, char *name)
 	metrics = pango_context_get_metrics (context, xtext->font->font, lang);
 	xtext->font->ascent = pango_font_metrics_get_ascent (metrics) / PANGO_SCALE;
 	xtext->font->descent = pango_font_metrics_get_descent (metrics) / PANGO_SCALE;
+
+	/*
+	 * In later versions of pango, a font's height should be calculated like
+	 * this to account for line gap; a typical symptom of not doing so is
+	 * cutting off the underscore on some fonts.
+	 */
+#if PANGO_VERSION_CHECK(1, 44, 0)
+	xtext->fontsize = pango_font_metrics_get_height (metrics) / PANGO_SCALE + 1;
+#else
+	xtext->fontsize = xtext->font->ascent + xtext->font->descent;
+#endif
+
 	pango_font_metrics_unref (metrics);
 }
+
 static int
 backend_get_text_width_emph (GtkXText *xtext, guchar *str, int len, int emphasis)
 {
@@ -3479,8 +3492,6 @@ gtk_xtext_set_font (GtkXText *xtext, char *name)
 	if (xtext->font == NULL)
 		return FALSE;
 
-	xtext->fontsize = xtext->font->ascent + xtext->font->descent;
-
 	{
 		char *time_str;
 		int stamp_size = xtext_get_stamp_str (time(0), &time_str);