Fix focus bug in graphing mode and other small changes (#938)

* Fix some bugs

* Style fixes from prev PR

src/Calculator/Controls/MathRichEditBox.cpp

@@ -185,7 +185,7 @@ void MathRichEditBox::SubmitEquation(EquationSubmissionSource source)
         auto formatRequest = ref new MathRichEditBoxFormatRequest(newVal);
         FormatRequest(this, formatRequest);
 
-        if (!formatRequest->FormattedText->IsEmpty())
+        if (formatRequest->FormattedText != nullptr && !formatRequest->FormattedText->IsEmpty())
         {
             newVal = formatRequest->FormattedText;
         }

src/Calculator/Controls/MathRichEditBox.h

@@ -39,8 +39,8 @@ namespace CalculatorApp
 
         public:
             MathRichEditBoxFormatRequest(Platform::String^ originalText)
+                : m_OriginalText(originalText)
             {
-                m_OriginalText = originalText;
             }
         };