brand only once, fix z4 interpreter bug

cursor position wasn't reset, leading to hanging indent after custom
prompt

src/onbeyond/z4/z4.s

@@ -457,6 +457,10 @@ call80          jsr     $c300
                 rts
 
 brand           jsr     $dbda
+                lda     #$da
+                sta     $ddf0
+                lda     #$db
+                sta     $ddf1
                 lda     #$17
                 sta     $25
                 lda     #0

src/onbeyond/z5/z5.s

@@ -452,6 +452,10 @@ call80          jsr     $c300
                 rts
 
 brand           jsr     $db5b
+                lda     #$5b
+                sta     $ddb6
+                lda     #$db
+                sta     $ddb7
                 lda     #$17
                 sta     $25
                 lda     #0