patch 8.1.0400: using freed memory with :diffget

Problem:    Using freed memory with :diffget.
Solution:   Skip ex_diffupdate() while updating diffs. (closes #3442)

Author: brammool

src/diff.c

@@ -21,7 +21,8 @@
 
 #if defined(FEAT_DIFF) || defined(PROTO)
 
-static int	diff_busy = FALSE;	/* ex_diffgetput() is busy */
+static int diff_busy = FALSE;	    // using diff structs, don't change them
+static int diff_need_update = FALSE; // ex_diffupdate needs to be called
 
 /* flags obtained from the 'diffopt' option */
 #define DIFF_FILLER	0x001	// display filler lines
@@ -908,6 +909,12 @@ ex_diffupdate(exarg_T *eap)	// "eap" can be NULL
     int		idx_new;
     diffio_T	diffio;
 
+    if (diff_busy)
+    {
+	diff_need_update = TRUE;
+	return;
+    }
+
     // Delete all diffblocks.
     diff_clear(curtab);
     curtab->tp_diff_invalid = FALSE;
@@ -2660,7 +2667,7 @@ ex_diffgetput(exarg_T *eap)
 	if (diff_buf_idx(curbuf) != idx_to)
 	{
 	    EMSG(_("E787: Buffer changed unexpectedly"));
-	    return;
+	    goto theend;
 	}
     }
 
@@ -2831,7 +2838,13 @@ ex_diffgetput(exarg_T *eap)
 	aucmd_restbuf(&aco);
     }
 
+theend:
     diff_busy = FALSE;
+    if (diff_need_update)
+    {
+	diff_need_update = FALSE;
+	ex_diffupdate(NULL);
+    }
 
     /* Check that the cursor is on a valid character and update it's position.
      * When there were filler lines the topline has become invalid. */

src/version.c

@@ -794,6 +794,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    400,
 /**/
     399,
 /**/