examples: fix some krazy warnings

doc/examples/addressbook-sdk/part2/addressbook.cpp

@@ -95,7 +95,7 @@ void AddressBook::submitContact()
     QString name = ui->nameLine->text();
     QString address = ui->addressText->toPlainText();
 
-    if (name == "" || address == "") {
+    if (name.isEmpty() || address.isEmpty()) {
         QMessageBox::information(this, tr("Empty Field"),
             tr("Please enter a name and address."));
         return;

doc/examples/addressbook-sdk/part3/addressbook.cpp

@@ -102,7 +102,7 @@ void AddressBook::submitContact()
     QString name = ui->nameLine->text();
     QString address = ui->addressText->toPlainText();
 
-    if (name == "" || address == "") {
+    if (name.isEmpty() || address.isEmpty()) {
         QMessageBox::information(this, tr("Empty Field"),
             tr("Please enter a name and address."));
         return;

doc/examples/addressbook-sdk/part4/addressbook.cpp

@@ -101,7 +101,7 @@ void AddressBook::submitContact()
     QString name = ui->nameLine->text();
     QString address = ui->addressText->toPlainText();
 
-    if (name == "" || address == "") {
+    if (name.isEmpty() || address.isEmpty()) {
         QMessageBox::information(this, tr("Empty Field"),
             tr("Please enter a name and address."));
     }

doc/examples/addressbook-sdk/part5/addressbook.cpp

@@ -96,7 +96,7 @@ void AddressBook::submitContact()
     QString name = ui->nameLine->text();
     QString address = ui->addressText->toPlainText();
 
-    if (name == "" || address == "") {
+    if (name.isEmpty() || address.isEmpty()) {
         QMessageBox::information(this, tr("Empty Field"),
             tr("Please enter a name and address."));
         updateInterface(NavigationMode);

doc/examples/addressbook-sdk/part6/addressbook.cpp

@@ -102,7 +102,7 @@ void AddressBook::submitContact()
     QString name = ui->nameLine->text();
     QString address = ui->addressText->toPlainText();
 
-    if (name == "" || address == "") {
+    if (name.isEmpty() || address.isEmpty()) {
         QMessageBox::information(this, tr("Empty Field"),
             tr("Please enter a name and address."));
         updateInterface(NavigationMode);

doc/examples/addressbook-sdk/part7/addressbook.cpp

@@ -99,7 +99,7 @@ void AddressBook::submitContact()
     QString name = ui->nameLine->text();
     QString address = ui->addressText->toPlainText();
 
-    if (name == "" || address == "") {
+    if (name.isEmpty() || address.isEmpty()) {
         QMessageBox::information(this, tr("Empty Field"),
             tr("Please enter a name and address."));
         updateInterface(NavigationMode);