Stop some of the pointless overflows in three-column mode

Essentially: Tell flex it can shrink the content, too, with some
weird voodoo.

bug: T201126
Change-Id: Ic54dd9b7d499d0be6653767525cc2015350c8ed7

resources/screen-desktop-full.less

@@ -12,6 +12,8 @@
 
 #mw-content-wrapper {
 	.flex(1, 1, auto, 2);
+	// Make word wrapping, max-width percentages, etc work with the above flex
+	min-width: 50%;
 }
 
 #mw-related-navigation {