[NETBEANS-7981] Handling Diagnostics with position -1 while writing error/warning index.

[lahodaj]

When code like:

package javaapplication2;

public class JavaApplication2 {

    public static void main(String[] args) {
        new G() {
            
        };
    }
    
}

class G {
    @Deprecated
    G() {}
}

is indexed with -Xlint:deprecation, writing error/warning index may fail due to an exception like:

java.lang.ArrayIndexOutOfBoundsException: Index -1 out of bounds for length 605
	at com.sun.tools.javac.util.Position$LineTabMapImpl.getColumnNumber(Position.java:266)
	at com.sun.tools.javac.util.Position$LineMapImpl.getColumnNumber(Position.java:236)
	at com.sun.tools.javac.util.Position$LineTabMapImpl.getColumnNumber(Position.java:253)
	at org.netbeans.modules.java.source.indexing.JavaCustomIndexer$ErrorConvertorImpl.getRange(JavaCustomIndexer.java:1329)

This is because the Diagnostics has end position -1. This patch simply proposes to treat this case as a missing end position.

Separately, it should be investigated if javac should produce errors or warnings like this.