GUI2/Message: tweaked Magic Numbers to fix layout failure with large portraits

[ci skip]

Fixes #2912

changelog.md

@@ -103,6 +103,7 @@
      unlike in 1.12 (issue #3033).
    * Fixed the first unit sometimes not being selected when opening the Recall
      dialog.
+   * Fixed a crash when using very large portraits in [message] (issue #2912)
  ### WML engine
    * Support formula= key in [variable] ConditionalWML
    * Support to_location in [move_unit], taking a location ID

data/gui/window/wml_message.cfg

@@ -36,7 +36,13 @@ where
 				0
 			)
 		),
-		max_height = (gamemap_height - 4)
+		# TODO: this is rather hacky. The old value was gamemap_height - 4 but that caused
+		# crashes with the 727 px high Rithrandil portrait in TRoW. This value seems to work,
+		# but the fact that it crashed at all points to some deeper logic flaw in the size
+		# calculation formulas here. Need to revisit at some point...
+		#
+		# -- vultraz, 2018-05-24
+		max_height = (gamemap_height - 30)
 	)
 )#enddef