Improve error handling

Do not use `sqlite3_errmsg` when `sqlite3_errcode` doesn't match
result code.
Use `sqlite3_errstr` instead.

src/main/java/org/sqlite/SQLite.java

@@ -65,6 +65,7 @@ public final class SQLite implements Library {
 	// Applications can use the sqlite3_log(E,F,..) API to send new messages to the log, if desired, but this is discouraged.
 	public static native void sqlite3_log(int iErrCode, String msg);
 
+	static native String sqlite3_errstr(int rc);
 	static native String sqlite3_errmsg(SQLite3 pDb); // copy needed: the error string might be overwritten or deallocated by subsequent calls to other SQLite interface functions.
 	static native int sqlite3_errcode(SQLite3 pDb);
 

src/main/java/org/sqlite/SQLiteException.java

@@ -39,8 +39,12 @@ public SQLiteException(Conn c, String reason, int errCode, Throwable cause) {
 		super(reason, null, errCode, cause);
 		if (c == null) {
 			errMsg = null;
-		} else if (getErrorCode() >= 0) {
-			errMsg = c.getErrMsg();
+		} else if (errCode >= 0) {
+			if (c.getErrCode() == errCode) {
+				errMsg = c.getErrMsg();
+			} else {
+				errMsg = SQLite.sqlite3_errstr(errCode);
+			}
 		} else {
 			errMsg = null;
 		}

src/main/java/org/sqlite/driver/Guard.java

@@ -41,7 +41,7 @@ static void closeAll(AutoCloseable... acs) throws SQLException {
 
 	void close() throws SQLException;
 
-	class SneakyGuard<T> implements AutoCloseable, Runnable {
+	class SneakyGuard implements AutoCloseable, Runnable {
 		private final Guard guard;
 		public SneakyGuard(Guard guard) {
 			this.guard = guard;