zasm: make DE indicate the last line to be read

Facilitates debugging

apps/zasm/main.asm

@@ -88,10 +88,14 @@ incOutputOffset:
 	pop	de
 	ret
 
+; Repeatedly reads lines from IO, assemble them and spit the binary code in
+; IO. Z is set on success, unset on error. DE contains the last line number to
+; be read (first line is 1).
 zasmParseFile:
-	ld	hl, 0
-	ld	(curOutputOffset), hl
+	ld	de, 0
+	ld	(curOutputOffset), de
 .loop:
+	inc	de
 	call	ioReadLine
 	or	a		; is A 0?
 	ret	z		; We have EOF

tools/emul/zasm.c

@@ -119,6 +119,7 @@ int main()
     }
 #endif
     fflush(stdout);
+    fprintf(stderr, "Ended with A=%d DE=%d\n", cpu.R1.br.A, cpu.R1.wr.DE);
     return 0;
 }