sap.m.SelectDialog: Allow clear in single selection

The clear button is always enabled now, if showClearButton=true and multiSelect=false.
The clear button behavior is redefined to act as clear+confirm in single selection mode.

src/sap.m/src/sap/m/SelectDialog.js

@@ -1017,7 +1017,19 @@ function(
 				press: function() {
 					this._removeSelection();
 					this._updateSelectionIndicator();
-					this._oDialog.focus();
+					if (this.getMultiSelect()) {
+						this._oDialog.focus();
+					} else {
+						fnClearAfterClose = function () {
+							this._oSelectedItem = this._oList.getSelectedItem();
+							this._aSelectedItems = this._oList.getSelectedItems();
+
+							this._oDialog.detachAfterClose(fnClearAfterClose);
+							this._fireConfirmAndUpdateSelection();
+						}.bind(this);
+						this._oDialog.attachAfterClose(fnClearAfterClose);
+						this._oDialog.close();
+					}
 				}.bind(this)
 			});
 		}
@@ -1064,7 +1076,7 @@ function(
 			oInfoBar = this._oList.getInfoToolbar();
 
 		if (this.getShowClearButton() && this._oClearButton) {
-			this._oClearButton.setEnabled(iSelectedContexts > 0);
+			this._oClearButton.setEnabled(iSelectedContexts > 0 || !this.getMultiSelect());
 		}
 		// update the selection label
 		oInfoBar.setVisible(!!iSelectedContexts && this.getMultiSelect());