fix draw-bitmap result to match docs

collects/racket/draw/private/bitmap-dc.rkt

@@ -147,7 +147,8 @@
             [sy (if (zero? src-h) 1.0 (/ dest-h src-h))])
         (let ([t (get-transformation)])
           (scale sx sy)
-          (draw-bitmap-section src (/ dest-x sx) (/ dest-y sy) src-x src-y src-w src-h style color mask)
-          (set-transformation t))))))
+          (begin0
+           (draw-bitmap-section src (/ dest-x sx) (/ dest-y sy) src-x src-y src-w src-h style color mask)
+           (set-transformation t)))))))
 
 (install-bitmap-dc-class! bitmap-dc%)

collects/racket/draw/private/dc.rkt

@@ -1594,7 +1594,8 @@
            (stamp-pattern src a-src-x a-src-y)])
          (when clip-mask
            (cairo_restore cr))
-         (flush-cr))))
+         (flush-cr)))
+      #t)
 
     (define/private (bitmap-to-b&w-bitmap src src-x src-y src-w src-h style color mask)
       (let* ([bm-w (inexact->exact (ceiling src-w))]