fastboot: get rid of manual transport memory management

Existing code has transport memory leaks. Use smart pointers
for transport to get rid of those cases and manual memory
management

Test: atest fastboot_test
Test: manually checked transport isn't leaking anymore
Bug: 296629925
Change-Id: Ifdf162d5084f61ae5c1d2b56a897464af58100da
Signed-off-by: Dmitrii Merkurev <dimorinny@google.com>
diff --git a/fastboot/usb_osx.cpp b/fastboot/usb_osx.cpp
index 8b852f5..28300b2 100644
--- a/fastboot/usb_osx.cpp
+++ b/fastboot/usb_osx.cpp
@@ -469,16 +469,20 @@
 /*
  * Definitions of this file's public functions.
  */
-
-UsbTransport* usb_open(ifc_match_func callback, uint32_t timeout_ms) {
+std::unique_ptr<UsbTransport> usb_open(ifc_match_func callback, uint32_t timeout_ms) {
+    std::unique_ptr<UsbTransport> result;
     std::unique_ptr<usb_handle> handle;
 
     if (init_usb(callback, &handle) < 0) {
         /* Something went wrong initializing USB. */
-        return nullptr;
+        return result;
     }
 
-    return new OsxUsbTransport(std::move(handle), timeout_ms);
+    if (handle) {
+        result = std::make_unique<OsxUsbTransport>(std::move(handle), timeout_ms);
+    }
+
+    return result;
 }
 
 OsxUsbTransport::~OsxUsbTransport() {