mysqlc: resultset's previous() on first position..

.. should move the cursor backwards to beforeFirst position and return
false.

Change-Id: Icbb4bed0ea39ea3a0bf375d5616e3ef768fc69d9
Reviewed-on: https://gerrit.libreoffice.org/66729
Tested-by: Jenkins
Reviewed-by: Tamás Bunth <btomi96@gmail.com>

connectivity/qa/connectivity/mysql/mysql.cxx

@@ -256,6 +256,12 @@ void MysqlTestDriver::testDBPositionChange()
     xResultSet->first();
     CPPUNIT_ASSERT_EQUAL(1, xResultSet->getRow());
 
+    // Now previous should put the cursor to before-first position, but it
+    // should return with false.
+    successPrevious = xResultSet->previous();
+    CPPUNIT_ASSERT(!successPrevious);
+    CPPUNIT_ASSERT_EQUAL(0, xResultSet->getRow());
+
     nUpdateCount = xStatement->executeUpdate("DROP TABLE myTestTable");
     CPPUNIT_ASSERT_EQUAL(0, nUpdateCount); // it's a DDL statement
 }

connectivity/source/drivers/mysqlc/mysqlc_resultset.cxx

@@ -652,8 +652,15 @@ sal_Bool SAL_CALL OResultSet::previous()
     MutexGuard aGuard(m_aMutex);
     checkDisposed(OResultSet_BASE::rBHelper.bDisposed);
 
-    if (m_nRowPosition <= 0)
+    if (m_nRowPosition == 0)
+    {
+        m_nRowPosition--;
         return false;
+    }
+    else if (m_nRowPosition < 0)
+    {
+        return false;
+    }
 
     m_nRowPosition--;
     return true;