Fixed strreplace() to handle NULL strings

CONTRIBUTORS

@@ -3655,6 +3655,8 @@ J
  for reporting a possible discrepancy of the primary device number in the LSTD and
  PRIM commands
  for adding support for EAC3 audio from other sources
+ for reporting a crash if a pattern timer spawns a timer that uses EPISODE and the
+ event has no short text
 
 Stefan Verse <Verse@amotronics.de>
  for fixing an occasional black screen when switching channels

HISTORY

@@ -9562,3 +9562,7 @@ Video Disk Recorder Revision History
 - Fixed a compiler warning (thanks to Winfried Köhler).
 - Fixed convertCharacterTable() in case iconv_open() fails (thanks to Helmut Binder).
 - Official release.
+
+2021-01-02: Version 2.4.7
+
+- Fixed strreplace() to handle NULL strings (reported by Jürgen Schneider).

tools.c

@@ -4,7 +4,7 @@
  * See the main source file 'vdr.c' for copyright information and
  * how to reach the author.
  *
- * $Id: tools.c 4.13 2020/11/22 13:32:05 kls Exp $
+ * $Id: tools.c 4.13.1.1 2021/01/02 15:05:48 kls Exp $
  */
 
 #include "tools.h"
@@ -151,6 +151,8 @@ char *strreplace(char *s, char c1, char c2)
 
 char *strreplace(char *s, const char *s1, const char *s2)
 {
+  if (!s || !s1 || !s2)
+     return s;
   char *p = strstr(s, s1);
   if (p) {
      int of = p - s;