OPAL-2361: Catch magma exception when missing category cannot be cast to...

... a continuous valueType

Because, Magma has its own logic to compute the valueOf Double and Integer, I think its preferrable to catch the exception than to copy and apply the same logic. Here is what Magma does :

DecimalType.java (normalize replaces the ',' char with '.')
```java
try {
      return Factory.newValue(this, Double.valueOf(normalize(string)));
    } catch(NumberFormatException e) {
      throw new MagmaRuntimeException("Not a decimal value: " + string, e);
    }
```

IntegerType.java (normalize trims the string)
```java
try {
      return Strings.isNullOrEmpty(string) ? nullValue() : Factory.newValue(this, Long.valueOf(normalize(string)));
    } catch(NumberFormatException e) {
      throw new MagmaRuntimeException("Not a integer value: " + string, e);
    }
```