patch 8.0.0380: with 'linebreak' double wide char wraps badly

Problem:    With 'linebreak' set and 'breakat' includes ">" a double-wide
            character results in "<<" displayed.
Solution:   Check for the character not to be replaced. (Ozaki Kiichi,
            closes #1456)
diff --git a/src/screen.c b/src/screen.c
index d801c4c..cc9c9f6 100644
--- a/src/screen.c
+++ b/src/screen.c
@@ -4189,6 +4189,8 @@
 	}
 	else
 	{
+	    int c0;
+
 	    if (p_extra_free != NULL)
 	    {
 		vim_free(p_extra_free);
@@ -4197,7 +4199,7 @@
 	    /*
 	     * Get a character from the line itself.
 	     */
-	    c = *ptr;
+	    c0 = c = *ptr;
 #ifdef FEAT_MBYTE
 	    if (has_mbyte)
 	    {
@@ -4214,7 +4216,7 @@
 			/* Overlong encoded ASCII or ASCII with composing char
 			 * is displayed normally, except a NUL. */
 			if (mb_c < 0x80)
-			    c = mb_c;
+			    c0 = c = mb_c;
 			mb_utf8 = TRUE;
 
 			/* At start of the line we can have a composing char.
@@ -4538,7 +4540,8 @@
 		/*
 		 * Found last space before word: check for line break.
 		 */
-		if (wp->w_p_lbr && vim_isbreak(c) && !vim_isbreak(*ptr))
+		if (wp->w_p_lbr && c0 == c
+				      && vim_isbreak(c) && !vim_isbreak(*ptr))
 		{
 # ifdef FEAT_MBYTE
 		    int mb_off = has_mbyte ? (*mb_head_off)(line, ptr - 1) : 0;