patch 9.0.1183: 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 #11805)
diff --git a/src/indent.c b/src/indent.c
index cbb3f94..477a44d 100644
--- a/src/indent.c
+++ b/src/indent.c
@@ -2188,12 +2188,12 @@
 {
     int amount = get_the_indent();
 
-    if (amount >= 0)
-    {
-	change_indent(INDENT_SET, amount, FALSE, 0, TRUE);
-	if (linewhite(curwin->w_cursor.lnum))
-	    did_ai = TRUE;	// delete the indent if the line stays empty
-    }
+    if (amount < 0)
+	return;
+
+    change_indent(INDENT_SET, amount, FALSE, 0, TRUE);
+    if (linewhite(curwin->w_cursor.lnum))
+	did_ai = TRUE;	// delete the indent if the line stays empty
 }
 
 /*