xml.syntax: parse <-variable->s with parse-word instead of search so the no-word error gets properly raised when variable doesn't exist

basis/xml/syntax/syntax.factor

@@ -145,7 +145,7 @@ MACRO: interpolate-xml ( xml -- quot )
     ] each-interpolated drop ;
 
 : >search-hash ( seq -- hash )
-    [ dup search ] H{ } map>assoc ;
+    [ dup parse-word ] H{ } map>assoc ;
 
 : extract-variables ( xml -- seq )
     [ [ var>> , ] each-interpolated ] { } make ;