init: disallow reindex-chainstate when pruning

This fixes a bug where the node would be stuck in an
endless loop when combining these parameters.

test/functional/feature_pruning.py

@@ -141,6 +141,10 @@ class PruneTest(BitcoinTestFramework):
             expected_msg='Error: Prune mode is incompatible with -coinstatsindex.',
             extra_args=['-prune=550', '-coinstatsindex'],
         )
+        self.nodes[0].assert_start_raises_init_error(
+            expected_msg='Error: Prune mode is incompatible with -reindex-chainstate. Use full -reindex instead.',
+            extra_args=['-prune=550', '-reindex-chainstate'],
+        )
 
     def test_height_min(self):
         assert os.path.isfile(os.path.join(self.prunedir, "blk00000.dat")), "blk00000.dat is missing, pruning too early"