bzip2.c: Check argc >= 1 && argv[0] != NULL

This should never happen, but if there is no, or a NULL argv[0] then
use a hard coded string "bzip2" when calling copyFileName to define
progNameReally.

https://sourceware.org/bugzilla/show_bug.cgi?id=33046
diff --git a/bzip2.c b/bzip2.c
index 9ef7536..0c4445c 100644
--- a/bzip2.c
+++ b/bzip2.c
@@ -1825,7 +1825,11 @@
    copyFileName ( inName,  (Char*)"(none)" );
    copyFileName ( outName, (Char*)"(none)" );
 
-   copyFileName ( progNameReally, argv[0] );
+   if (argc >= 1 && argv[0] != NULL)
+      copyFileName ( progNameReally, argv[0] );
+   else
+      copyFileName ( progNameReally, (Char*)"bzip2" );
+
    progName = &progNameReally[0];
    for (tmp = &progNameReally[0]; *tmp != '\0'; tmp++)
       if (*tmp == PATH_SEP) progName = tmp + 1;