patch 9.0.1166: code is indented more than necessary

Problem:    Code is indented more than necessary.
Solution:   Use an early return where it makes sense. (Yegappan Lakshmanan,
            closes #11792)
diff --git a/src/edit.c b/src/edit.c
index 4a89fe1..983f1ac 100644
--- a/src/edit.c
+++ b/src/edit.c
@@ -2970,12 +2970,12 @@
     if (last_insert == NULL)
 	return NULL;
     s = vim_strsave(last_insert + last_insert_skip);
-    if (s != NULL)
-    {
-	len = (int)STRLEN(s);
-	if (len > 0 && s[len - 1] == ESC)	// remove trailing ESC
-	    s[len - 1] = NUL;
-    }
+    if (s == NULL)
+	return NULL;
+
+    len = (int)STRLEN(s);
+    if (len > 0 && s[len - 1] == ESC)	// remove trailing ESC
+	s[len - 1] = NUL;
     return s;
 }