Fix parsing conn string with a trailing comma

When connection string includes a trailing comma, existing impl in
Connect::ParseInputStr was doing an early exit without setting DSN
value to dbc->dsn. Because of this DSN was not used and default
:memory: instance was created.

The problem is not OS specific, but was happening on Windows all the
time because Windows ODBC Driver Manager is appending comma to the
passed connection string when calling SQLDriverConnect.

test_connect_odbc was extended to cover the trailing comma and also
parameters overriding in connection string.

Fixes: duckdb#29, duckdb#48

src/connect/connect.cpp

@@ -80,13 +80,11 @@ SQLRETURN Connect::ParseInputStr() {
 		input_str.erase(0, row_pos + 1);
 	}
 
-	if (input_str.empty()) {
-		return SQL_SUCCESS;
-	}
-
-	SQLRETURN ret = FindKeyValPair(input_str);
-	if (ret != SQL_SUCCESS) {
-		return ret;
+	if (!input_str.empty()) {
+		SQLRETURN ret = FindKeyValPair(input_str);
+		if (ret != SQL_SUCCESS) {
+			return ret;
+		}
 	}
 
 	// Extract the DSN from the config map as it is needed to read from the .odbc.ini file

test/tests/connect_with_ini.cpp

@@ -26,3 +26,23 @@ TEST_CASE("Test SQLConnect with Ini File", "[odbc]") {
 	DISCONNECT_FROM_DATABASE(env, dbc);
 #endif
 }
+
+// Connect to the database using the ini file when connection string
+// has extra options and a trailing comma
+TEST_CASE("Test SQLConnect with Ini File with extra options", "[odbc]") {
+#if defined ODBC_LINK_ODBCINST || defined WIN32
+	// Connect to the database using the ini file
+	SQLHANDLE env;
+	SQLHANDLE dbc;
+	DRIVER_CONNECT_TO_DATABASE(env, dbc, "DSN=DuckDB;allow_unsigned_extensions=false;");
+
+	// Check that the database is set
+	CheckDatabase(dbc);
+
+	// Check that allow_unsigned_extensions is set from connection string
+	CheckConfig(dbc, "allow_unsigned_extensions", "false");
+
+	// Disconnect from the database
+	DISCONNECT_FROM_DATABASE(env, dbc);
+#endif
+}