vshCommandParse: placate coverity

There is no real leak here, but Coverity-Prevent thinks there is.
It does not see that while there are four ways to return from
vshCommandGetToken with VSH_TK_END, none of them results in allocation
of a result.
* tools/virsh.c (vshCommandParse): Add a (currently) useless VIR_FREE,
to ensure that we never leak when vshCommandGetToken returns VSH_TK_END.

tools/virsh.c

@@ -8222,8 +8222,10 @@ vshCommandParse(vshControl *ctl, char *cmdstr)
 
             str = end;
 
-            if (tk == VSH_TK_END)
+            if (tk == VSH_TK_END) {
+                VIR_FREE(tkdata);
                 break;
+            }
             if (tk == VSH_TK_ERROR)
                 goto syntaxError;