Address Issue 1570: Make comboboxes scrollable

Note: It appears that mLabel is never set by combo boxes, this should eventually be fixed.
Checking !getFirstSelected() is sufficient to test if we're in the list, however.

indra/llui/llcombobox.cpp

@@ -909,6 +909,19 @@ BOOL LLComboBox::handleUnicodeCharHere(llwchar uni_char)
 	return result;
 }
 
+BOOL LLComboBox::handleScrollWheel(S32 x, S32 y, S32 clicks)
+{
+	if (mList->getVisible()) return mList->handleScrollWheel(x, y, clicks);
+	if (mAllowTextEntry) // We might be editable
+		if (!mList->getFirstSelected()) // We aren't in the list, don't kill their text
+			return false;
+
+	setCurrentByIndex(llclamp(getCurrentIndex() + clicks, 0, getItemCount() - 1));
+	prearrangeList();
+	onCommit();
+	return true;
+}
+
 void LLComboBox::setAllowTextEntry(BOOL allow, S32 max_chars, BOOL set_tentative)
 {
 	mAllowTextEntry = allow;

indra/llui/llcombobox.h

@@ -76,6 +76,7 @@ public:
 	virtual BOOL	handleToolTip(S32 x, S32 y, std::string& msg, LLRect* sticky_rect);
 	virtual BOOL	handleKeyHere(KEY key, MASK mask);
 	virtual BOOL	handleUnicodeCharHere(llwchar uni_char);
+	virtual BOOL	handleScrollWheel(S32 x, S32 y, S32 clicks);
 
 	// LLUICtrl interface
 	virtual void	clear();					// select nothing