Fixed SKIP not being allowed as a guard without a precondition

frontends/ParseOccam.hs

@@ -1907,6 +1907,10 @@ guard
     =   do m <- md
            (c, im) <- input
            return $ A.Alternative m (A.True m) c im
+    <|> do m <- md
+           sSKIP
+           eol
+           return $ A.AlternativeSkip m (A.True m)
     <|> do m <- md
            b <- tryVX expression sAmp
            do { (c, im) <- input; return $ A.Alternative m b c im }