findsubckt(), exclude the terminating '\0' from the search

src/frontend/numparam/xpressn.c

@@ -556,6 +556,7 @@ findsubckt(dico_t *dico, const char * const s)
 
     spice_dstring_init(&ustr);
 
+    k_ptr--;
     while ((k_ptr >= s) && (*k_ptr <= ' '))
         k_ptr--;