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/if_python.c b/src/if_python.c
index 90f75ec..863e931 100644
--- a/src/if_python.c
+++ b/src/if_python.c
@@ -1393,34 +1393,31 @@
     void
 python_buffer_free(buf_T *buf)
 {
-    if (BUF_PYTHON_REF(buf) != NULL)
-    {
-	BufferObject *bp = BUF_PYTHON_REF(buf);
-	bp->buf = INVALID_BUFFER_VALUE;
-	BUF_PYTHON_REF(buf) = NULL;
-    }
+    BufferObject *bp = BUF_PYTHON_REF(buf);
+    if (bp == NULL)
+	return;
+    bp->buf = INVALID_BUFFER_VALUE;
+    BUF_PYTHON_REF(buf) = NULL;
 }
 
     void
 python_window_free(win_T *win)
 {
-    if (WIN_PYTHON_REF(win) != NULL)
-    {
-	WindowObject *wp = WIN_PYTHON_REF(win);
-	wp->win = INVALID_WINDOW_VALUE;
-	WIN_PYTHON_REF(win) = NULL;
-    }
+    WindowObject *wp = WIN_PYTHON_REF(win);
+    if (wp == NULL)
+	return;
+    wp->win = INVALID_WINDOW_VALUE;
+    WIN_PYTHON_REF(win) = NULL;
 }
 
     void
 python_tabpage_free(tabpage_T *tab)
 {
-    if (TAB_PYTHON_REF(tab) != NULL)
-    {
-	TabPageObject *tp = TAB_PYTHON_REF(tab);
-	tp->tab = INVALID_TABPAGE_VALUE;
-	TAB_PYTHON_REF(tab) = NULL;
-    }
+    TabPageObject *tp = TAB_PYTHON_REF(tab);
+    if (tp == NULL)
+	return;
+    tp->tab = INVALID_TABPAGE_VALUE;
+    TAB_PYTHON_REF(tab) = NULL;
 }
 
     static int