Add missing null checks after allocations.

Bug: http://b/20317729
Change-Id: I62bb761d48ee59a1f4ddd0cdd0632432305ca2ca
diff --git a/adb/usb_osx.cpp b/adb/usb_osx.cpp
index 303ae45..a795ce3 100644
--- a/adb/usb_osx.cpp
+++ b/adb/usb_osx.cpp
@@ -336,6 +336,7 @@
         goto err_bad_adb_interface;
 
     handle = reinterpret_cast<usb_handle*>(calloc(1, sizeof(usb_handle)));
+    if (handle == nullptr) goto err_bad_adb_interface;
 
     //* Iterate over the endpoints for this interface and find the first
     //* bulk in/out pipes available.  These will be our read/write pipes.