patch 8.0.0374: invalid memory access when using :sc in Ex mode

Problem:    Invalid memory access when using :sc in Ex mode. (Dominique Pelle)
Solution:   Avoid the column being negative.  Also fix a hang in Ex mode.
diff --git a/src/ex_getln.c b/src/ex_getln.c
index 3c40ff7..9180319 100644
--- a/src/ex_getln.c
+++ b/src/ex_getln.c
@@ -2369,9 +2369,16 @@
 	if (ga_grow(&line_ga, 40) == FAIL)
 	    break;
 
-	/* Get one character at a time. */
+	/*
+	 * Get one character at a time.
+	 */
 	prev_char = c1;
-	c1 = vgetc();
+
+	/* Check for a ":normal" command and no more characters left. */
+	if (ex_normal_busy > 0 && typebuf.tb_len == 0)
+	    c1 = '\n';
+	else
+	    c1 = vgetc();
 
 	/*
 	 * Handle line editing.