fix #H2785 - engraving punctuation

Message tidbit when engraving with a weapon which becomes too dull to
finish the whole text:  add missing final period to
  You are only able to write "<partial text>".
I think that proper usage puts the period in front of the quote rather than
after, but that could make it look as if the period ended up inside the
partial engraving.

src/engrave.c

@@ -1115,7 +1115,7 @@ doengrave()
 	    if (!maxelen && *sp) {
 		*sp = (char)0;
 		if (multi) nomovemsg = "You cannot write any more.";
-		You("only are able to write \"%s\"", ebuf);
+		You("only are able to write \"%s\".", ebuf);
 	    }
 	}