MDEV-22387: Do not violate __attribute__((nonnull))

This follows up commit
commit 94a520ddbe39ae97de1135d98699cf2674e6b77e and
commit 7c5519c12d46ead947d341cbdcbb6fbbe4d4fe1b.

After these changes, the default test suites on a
cmake -DWITH_UBSAN=ON build no longer fail due to passing
null pointers as parameters that are declared to never be null,
but plenty of other runtime errors remain.

1 files changed, 7 insertions, 4 deletions

diff --git a/sql/sql_string.cc b/sql/sql_string.cc
index b79ca82698b..4e0c7aea84b 100644
--- a/sql/sql_string.cc
+++ b/sql/sql_string.cc
@@ -1,5 +1,5 @@
 /* Copyright (c) 2000, 2013, Oracle and/or its affiliates.
-   Copyright (c) 2016, MariaDB
+   Copyright (c) 2016, 2020, MariaDB
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -175,8 +175,8 @@ bool String::copy(const String &str)
 {
   if (alloc(str.str_length))
     return TRUE;
-  str_length=str.str_length;
-  bmove(Ptr,str.Ptr,str_length);		// May be overlapping
+  if ((str_length=str.str_length))
+    bmove(Ptr,str.Ptr,str_length);		// May be overlapping
   Ptr[str_length]=0;
   str_charset=str.str_charset;
   return FALSE;
@@ -539,8 +539,11 @@ bool String::append_ulonglong(ulonglong val)
 
 bool String::append(const char *s,uint32 arg_length, CHARSET_INFO *cs)
 {
+  if (!arg_length)
+    return false;
+
   uint32 offset;
-  
+
   if (needs_conversion(arg_length, cs, str_charset, &offset))
   {
     uint32 add_length;