protect against 0 width in string:wrap()

library/lua/dfhack.lua

@@ -439,6 +439,7 @@ end
 -- multiple lines. If width is not specified, 72 is used.
 function string:wrap(width)
     width = width or 72
+    if width <= 0 then error('expected width > 0; got: '..tostring(width)) end
     local wrapped_text = {}
     for line in self:gmatch('[^\n]*') do
         local line_start_pos = 1

library/lua/gui/widgets.lua

@@ -558,7 +558,8 @@ WrappedLabel.ATTRS{
 }
 
 function WrappedLabel:getWrappedText(width)
-    if not self.text_to_wrap then return nil end
+    -- 0 width can happen if the parent has 0 width
+    if not self.text_to_wrap or width <= 0 then return nil end
     local text_to_wrap = getval(self.text_to_wrap)
     if type(text_to_wrap) == 'table' then
         text_to_wrap = table.concat(text_to_wrap, NEWLINE)

test/library/string.lua

@@ -67,6 +67,8 @@ function test.wrap()
     expect.eq('hel\nlo\nwor\nld', ('hello world'):wrap(3))
     expect.eq('hel\nloo\nwor\nldo', ('helloo  worldo'):wrap(3))
     expect.eq('', (''):wrap())
+
+    expect.error_match('expected width > 0', function() ('somestr'):wrap(0) end)
 end
 
 function test.escape_pattern()