Fixed a crash that happened when attempting to select text with left key + shift

Modules/Contents/UI/Source/PolyUITextInput.cpp

@@ -1123,7 +1123,9 @@ void UITextInput::onKeyDown(PolyKEY key, wchar_t charCode) {
 						if(selectionCaretPosition > 0)
 							setSelection(lineOffset, selectionLine, this->caretPosition, selectionCaretPosition-1);
 					} else {
-						setSelection(lineOffset, lineOffset, caretPosition, caretPosition-1);
+						if (caretPosition > 0) {
+							setSelection(lineOffset, lineOffset, caretPosition, caretPosition-1);
+						}
 					}
 				} else {
 					int newLineStart = lineOffset;