Internal error when replacing an non-existing extension with an empty extension

[jurgenvinju]

Describe the bug

rascal>|relative:///IDE|[extension=""]
java.lang.StringIndexOutOfBoundsException: begin 0, end -1, length 4
(internal error)
        at $shell$(|main://$shell$|)

java.lang.StringIndexOutOfBoundsException: begin 0, end -1, length 4
        at java.base/java.lang.String.checkBoundsBeginEnd(String.java:3319)
        at java.base/java.lang.String.substring(String.java:1874)
        at org.rascalmpl.interpreter.result.SourceLocationResult.fieldUpdate(SourceLocationResult.java:503)
        at org.rascalmpl.semantics.dynamic.Expression$FieldUpdate.interpret(Expression.java:941)