lua fix potential null warning

I'm not sure this would happen but I suspect its possible to get malformed
data back from lineinfo as this is how the error system tracks code flow
and this is a hacked add-on to allow RLE (run length encoding) of
said code flow data

Change-Id: I4b914c632935f8b1a9fa960212c58e810b2db738

apps/plugins/lua/lcode.c

@@ -802,8 +802,10 @@ static unsigned char *growLineInfo(FuncState *fs) {
                   unsigned char, MAX_INT, "code size overflow");
 
   p = &f->packedlineinfo[start];
+  if (p && f->sizelineinfo > 0) {
     memset(p, INFO_FILL_BYTE, f->sizelineinfo - start);
     f->packedlineinfo[f->sizelineinfo - 1] = '\0';
+  }
   return p;
 }