[composer] Don't round down scale for maps if < 1 (fix #9366)

Author: nyalldawson

src/app/composer/qgscomposermapwidget.cpp

@@ -420,8 +420,24 @@ void QgsComposerMapWidget::updateGuiElements()
     blockAllSignals( true );
 
     //width, height, scale
-//    QRectF composerMapRect = mComposerMap->rect();
-    mScaleLineEdit->setText( QString::number( mComposerMap->scale(), 'f', 0 ) );
+    double scale = mComposerMap->scale();
+
+    //round scale to an appropriate number of decimal places
+    if ( scale >= 10 )
+    {
+      //round scale to integer if it's greater than 10
+      mScaleLineEdit->setText( QString::number( mComposerMap->scale(), 'f', 0 ) );
+    }
+    else if ( scale >= 1 )
+    {
+      //don't round scale if it's less than 10, instead use 4 decimal places
+      mScaleLineEdit->setText( QString::number( mComposerMap->scale(), 'f', 4 ) );
+    }
+    else
+    {
+      //if scale < 1 then use 10 decimal places
+      mScaleLineEdit->setText( QString::number( mComposerMap->scale(), 'f', 10 ) );
+    }
 
     //preview mode
     QgsComposerMap::PreviewMode previewMode = mComposerMap->previewMode();

src/core/composer/qgscomposermap.cpp

@@ -781,7 +781,7 @@ void QgsComposerMap::setNewScale( double scaleDenominator )
 {
   double currentScaleDenominator = scale();
 
-  if ( scaleDenominator == currentScaleDenominator )
+  if ( scaleDenominator == currentScaleDenominator || scaleDenominator == 0 )
   {
     return;
   }