Fix CID 471656 in smb_addfile_withlist()

No one's using this function currently (and may never).

It was used back when I was putting archive contents in .ini format in the
files' metadata (now auxdata).

src/smblib/smbfile.c

@@ -361,11 +361,13 @@ int smb_addfile_withlist(smb_t* smb, smbfile_t* file, int storage, const char* e
 
 	if(list != NULL && *list != NULL) {
 		size_t size = strListCount(list) * 1024;
+		if(size > 0) {
 			auxdata = calloc(1, size);
 			if(auxdata == NULL)
 				return SMB_ERR_MEM;
 			strListCombine(list, auxdata, size - 1, "\r\n");
 		}
+	}
 	result = smb_addfile(smb, file, storage, extdesc, auxdata, path);
 	free(auxdata);
 	return result;