2015-04-10: catch source-properties error for line ending in colon (empty final

catch source-properties error for line ending in colon (empty final parens).

diff --git a/wisp-scheme.w b/wisp-scheme.w
--- a/wisp-scheme.w
+++ b/wisp-scheme.w
@@ -380,7 +380,11 @@ define : line-finalize line
                  line-strip-lone-colon
                    line-strip-continuation line
          when : not : null? : source-properties line
-                set-source-properties! l : source-properties line
+                catch #t
+                  lambda ()
+                    set-source-properties! l : source-properties line
+                  lambda : key . arguments
+                    . #f
          . l
 
 define : wisp-add-source-properties-from source target