Have infback() deliver all of the available output up to any error.

infback.c

@@ -606,25 +606,27 @@ void FAR *out_desc;
             break;
 
         case DONE:
-            /* inflate stream terminated properly -- write leftover output */
+            /* inflate stream terminated properly */
             ret = Z_STREAM_END;
-            if (left < state->wsize) {
-                if (out(out_desc, state->window, state->wsize - left))
-                    ret = Z_BUF_ERROR;
-            }
             goto inf_leave;
 
         case BAD:
             ret = Z_DATA_ERROR;
             goto inf_leave;
 
-        default:                /* can't happen, but makes compilers happy */
+        default:
+            /* can't happen, but makes compilers happy */
             ret = Z_STREAM_ERROR;
             goto inf_leave;
         }
 
-    /* Return unused input */
+    /* Write leftover output and return unused input */
   inf_leave:
+    if (left < state->wsize) {
+        if (out(out_desc, state->window, state->wsize - left) &&
+            ret == Z_STREAM_END)
+            ret = Z_BUF_ERROR;
+    }
     strm->next_in = next;
     strm->avail_in = have;
     return ret;