fix crash when entering non digits in the input fields

MainWindow.xaml.cs

@@ -36,19 +36,14 @@ namespace PhysFormuler
         {
             if (box.Text != "")
             {
-                if (Convert.ToDouble(box.Text) != 0)
+                double number;
+                if (Double.TryParse(box.Text,out number))
                 {
-                    return true;
+                    return !double.IsNaN(number);
                 }
-                else
+                else return false;
-                {
-                    return false;
-                }
-            }
-            else
-            {
-                return false;
             }
+            else return false;
         }
 
         private void Update(string type)

PhysFormuler.csproj.user

@@ -10,4 +10,7 @@
     <FallbackCulture>ru-RU</FallbackCulture>
     <VerifyUploadedFiles>false</VerifyUploadedFiles>
   </PropertyGroup>
+  <PropertyGroup>
+    <EnableSecurityDebugging>false</EnableSecurityDebugging>
+  </PropertyGroup>
 </Project>