Fix emulator builds

which don't have boot.img.

Change-Id: Id97a53c5356d435d9c70107ef047bed003769e22

tools/releasetools/common.py

@@ -354,9 +354,12 @@ def GetBootableImage(name, prebuilt_name, unpack_dir, tree_subdir,
   else:
     print "building image from target_files %s..." % (tree_subdir,)
     fs_config = "META/" + tree_subdir.lower() + "_filesystem_config.txt"
-    return File(name, BuildBootableImage(os.path.join(unpack_dir, tree_subdir),
-                                         os.path.join(unpack_dir, fs_config),
-                                         info_dict))
+    data = BuildBootableImage(os.path.join(unpack_dir, tree_subdir),
+                              os.path.join(unpack_dir, fs_config),
+                              info_dict))
+    if data:
+      return File(name, data)
+    return None
 
 
 def UnzipTemp(filename, pattern=None):

tools/releasetools/make_recovery_patch

@@ -39,6 +39,9 @@ def main(argv):
   boot_img = common.GetBootableImage("boot.img", "boot.img",
                                      input_dir, "BOOT")
 
+  if not recovery_img or not boot_img:
+    sys.exit(0)
+
   def output_sink(fn, data):
     with open(os.path.join(output_dir, "SYSTEM", *fn.split("/")), "wb") as f:
       f.write(data)