Increment TARGET_WINDOWS_WRITTEN after stream_to_target_write.

Prior to this, TARGET_WINDOWS_WRITTEN would be incremented before
the call to stream_to_target_write if the target was nonzero size
and write_target succeeded. This caused tgt->start to be set
incorrectly. This confused mapio but not xdelta, leading to
correct target windows written to incorrect locations.

Change-Id: I76db5281a749a20d0e63b8126238eb1886d87a1c
diff --git a/syspatch.c b/syspatch.c
index a90e031..3b7b24c 100644
--- a/syspatch.c
+++ b/syspatch.c
@@ -196,10 +196,12 @@
     if (tgt->length) {
         if (write_target(tgt, target_state) != 0)
             return -1;
-        TARGET_WINDOWS_WRITTEN += 1;
     }
     if (stream_to_target_write(stream, tgt) != 0)
         return -1;
+    if (tgt->length) {
+        TARGET_WINDOWS_WRITTEN += 1;
+    }
     return 0;
 }