catch null vfork_exec_wrapper before it is too late

diff --git a/libs/pbd/system_exec.cc b/libs/pbd/system_exec.cc
index 811bd43d3907aded2701ba02581aa79c2f3186b8..01c46aa9eb62b603922aca904a1a3a3e0ceb34cf 100644 (file)
--- a/libs/pbd/system_exec.cc
+++ b/libs/pbd/system_exec.cc
@@ -805,6 +805,10 @@ SystemExec::start (int stderr_mode, const char *vfork_exec_wrapper)
 #else
        signal(SIGPIPE, SIG_DFL);
 #endif
+       if (!vfork_exec_wrapper) {
+               error << _("Cannot start external process, no vfork wrapper") << endmsg;
+               return -1;
+       }
 
        int good_fds[2] = { pok[1],  -1 };
        close_allv(good_fds);