refactor 'toDouble' extension method and use tryParse

VectoCommon/VectoCommon/Utils/StringExtensionMethods.cs

@@ -54,14 +54,17 @@ namespace TUGraz.VectoCommon.Utils
 				throw new FormatException("Cannot convert an empty string to a number.");
 			}
 
-			try {
-				return double.Parse(self, CultureInfo.InvariantCulture);
-			} catch (FormatException) {
+			var success = double.TryParse(self, out var retVal);
+			if (success) {
+				return retVal;
+			}
+
 			if (defaultValue.HasValue) {
 				return defaultValue.Value;
 			}
-				throw;
-			}
+
+			// throws an exception
+			return double.Parse(self, CultureInfo.InvariantCulture);
 		}
 
 		public static int ToInt(this string self, int? defaultValue = null)