Avoid some unnecessary dynamic_casts in QgsProject

...fixes Coverity warning

src/core/qgsproject.cpp

@@ -113,7 +113,7 @@ QgsProperty *findKey_( QString const &scope,
       {
         if ( nextProperty->isKey() )
         {
-          currentProperty = dynamic_cast<QgsPropertyKey*>( nextProperty );
+          currentProperty = static_cast<QgsPropertyKey*>( nextProperty );
         }
         else if ( nextProperty->isValue() && 1 == keySequence.count() )
         {
@@ -164,7 +164,8 @@ QgsProperty *addKey_( QString const &scope,
 
   // cursor through property key/value hierarchy
   QgsPropertyKey *currentProperty = rootProperty;
-  QgsProperty *newProperty; // link to next property down hiearchy
+  QgsProperty *nextProperty; // link to next property down hiearchy
+  QgsPropertyKey* newPropertyKey;
 
   while ( ! keySequence.isEmpty() )
   {
@@ -190,9 +191,9 @@ QgsProperty *addKey_( QString const &scope,
 
         return currentProperty;
       }
-      else if (( newProperty = currentProperty->find( keySequence.first() ) ) )
+      else if ( nextProperty = currentProperty->find( keySequence.first() ) )
       {
-        currentProperty = dynamic_cast<QgsPropertyKey*>( newProperty );
+        currentProperty = dynamic_cast<QgsPropertyKey*>( nextProperty );
 
         if ( currentProperty )
         {
@@ -205,11 +206,9 @@ QgsProperty *addKey_( QString const &scope,
       }
       else                // the next subkey doesn't exist, so add it
       {
-        newProperty = currentProperty->addKey( keySequence.first() );
-
-        if ( newProperty )
+        if ( newPropertyKey = currentProperty->addKey( keySequence.first() ) )
         {
-          currentProperty = dynamic_cast<QgsPropertyKey*>( newProperty );
+          currentProperty = newPropertyKey;
         }
         continue;
       }

src/core/qgsprojectproperty.cpp

@@ -305,8 +305,7 @@ void QgsPropertyKey::dump( int tabs ) const
     {
       if ( i.next().value()->isValue() )
       {
-        QgsPropertyValue * propertyValue =
-          dynamic_cast<QgsPropertyValue*>( i.value() );
+        QgsPropertyValue * propertyValue = static_cast<QgsPropertyValue*>( i.value() );
 
         if ( QVariant::StringList == propertyValue->value().type() )
         {