Assembler: duplicate labels in conditional IF...ELSE...ENDIF blocks + Fix

[Merilix]

Example

test	equ	0
	org	100h
	ld	de,msg1
	ld	c,9
	call	5
	jp	0
	if	test
msg1	db	'Hello Test$'
	else
msg1	db	'Hello World$'
	endif

The assembler complain about double label msg1 but shouldn't.
This fix works for me:
In Z80Assembler.java method parseLine (line #672)
replace
if( labelName != null ) {
with
if( labelName != null && isAssemblingEnabled()) {