config: separate the asmap finding and parsing checks

and update the tests.

src/init.cpp

@@ -1834,9 +1834,13 @@ bool AppInitMain(NodeContext& node)
         if (!asmap_path.is_absolute()) {
             asmap_path = GetDataDir() / asmap_path;
         }
+        if (!fs::exists(asmap_path)) {
+            InitError(strprintf(_("Could not find asmap file %s").translated, asmap_path));
+            return false;
+        }
         std::vector<bool> asmap = CAddrMan::DecodeAsmap(asmap_path);
         if (asmap.size() == 0) {
-            InitError(strprintf(_("Could not find or parse specified asmap: '%s'").translated, asmap_path));
+            InitError(strprintf(_("Could not parse asmap file '%s'").translated, asmap_path));
             return false;
         }
         const uint256 asmap_version = SerializeHash(asmap);

test/functional/feature_asmap.py

@@ -75,7 +75,7 @@ class AsmapTest(BitcoinTestFramework):
     def test_default_asmap_with_missing_file(self):
         self.log.info('Test bitcoind -asmap with missing default map file')
         self.stop_node(0)
-        msg = "Error: Could not find or parse specified asmap: '\"{}\"'".format(self.default_asmap)
+        msg = "Error: Could not find asmap file '\"{}\"'".format(self.default_asmap)
         self.node.assert_start_raises_init_error(extra_args=['-asmap'], expected_msg=msg)
 
     def run_test(self):