Avoid a runtime check failure

Without the initialization, Windows could complain a runtime check
failure.

src/os/host-text.c

@@ -141,7 +141,7 @@ static u32* text_ext_words;
             u32 *words, *w;
             REBSER *obj;
             REBCNT type;
-            REBXYF caret, highlightStart, highlightEnd;
+			REBXYF caret, highlightStart, highlightEnd = {0, 0};
             REBXYF *pcaret = 0, *phighlightStart = 0;
             obj = RXA_OBJECT(frm, 1);
 //Reb_Print("RXI_WORDS_OF_OBJECT() called\n");