fixing segfault, reported on IRC #gentoo-vdr & vdr-portal.de
https://www.vdr-portal.de/forum/index.php?thread/132017-videotextuntertitel-f%C3%BCr-vdr-2-4-0/&postID=1306478#post1306478

Signed-Off-By: Joerg Bornkessel <hd_brummy@gentoo.org> ( 2020 Mar 02 )
diff -Naur vdr-2.4.1.orig/channels.c vdr-2.4.1/channels.c
--- vdr-2.4.1.orig/channels.c	2020-03-02 19:52:51.052496538 +0100
+++ vdr-2.4.1/channels.c	2020-03-02 19:54:05.096496538 +0100
@@ -429,7 +429,7 @@
   return Modified;
 }
 
-void cChannel::SetTeletextSubtitlePages(tTeletextSubtitlePage pages[], int numberOfPages)
+bool cChannel::SetTeletextSubtitlePages(tTeletextSubtitlePage pages[], int numberOfPages)
 {
   int mod = CHANNELMOD_NONE;
   LOCK_CHANNELS_WRITE;
@@ -447,7 +447,7 @@
       totalTtxtSubtitlePages++;
       }
   modification |= mod;
-  Channels->SetModified();
+  return true;
 }
 
 void cChannel::SetSeen(void)
diff -Naur vdr-2.4.1.orig/channels.h vdr-2.4.1/channels.h
--- vdr-2.4.1.orig/channels.h	2020-03-02 19:52:51.052496538 +0100
+++ vdr-2.4.1/channels.h	2020-03-02 19:54:31.745496538 +0100
@@ -212,7 +212,7 @@
   bool SetName(const char *Name, const char *ShortName, const char *Provider);
   bool SetPortalName(const char *PortalName);
   bool SetPids(int Vpid, int Ppid, int Vtype, int *Apids, int *Atypes, char ALangs[][MAXLANGCODE2], int *Dpids, int *Dtypes, char DLangs[][MAXLANGCODE2], int *Spids, char SLangs[][MAXLANGCODE2], int Tpid);
-  void SetTeletextSubtitlePages(tTeletextSubtitlePage pages[], int numberOfPages);
+  bool SetTeletextSubtitlePages(tTeletextSubtitlePage pages[], int numberOfPages);
   bool SetCaIds(const int *CaIds); // list must be zero-terminated
   bool SetCaDescriptors(int Level);
   bool SetLinkChannels(cLinkChannels *LinkChannels);
diff -Naur vdr-2.4.1.orig/pat.c vdr-2.4.1/pat.c
--- vdr-2.4.1.orig/pat.c	2020-03-02 19:52:51.053496538 +0100
+++ vdr-2.4.1/pat.c	2020-03-02 19:55:40.819496538 +0100
@@ -649,7 +649,7 @@
               if (manualPageNumber)
                  TeletextSubtitlePages[NumTPages++] = tTeletextSubtitlePage(manualPageNumber);
               }
-           Channel->SetTeletextSubtitlePages(TeletextSubtitlePages, NumTPages);
+           ChannelsModified |= Channel->SetTeletextSubtitlePages(TeletextSubtitlePages, NumTPages);
            ChannelsModified |= Channel->SetCaIds(CaDescriptors->CaIds());
            ChannelsModified |= Channel->SetSubtitlingDescriptors(SubtitlingTypes, CompositionPageIds, AncillaryPageIds);
            }