Fix crash when virtualbox list of VMS return an empty line

Fix #206

gns3server/modules/virtualbox/__init__.py

@@ -168,7 +168,7 @@ class VirtualBox(BaseManager):
         vms = []
         result = yield from self.execute("list", ["vms"])
         for line in result:
-            if line[0] != '"' or line[-1:] != "}":
+            if len(line) == 0 or line[0] != '"' or line[-1:] != "}":
                 continue # Broken output (perhaps a carriage return in VM name
             vmname, _ = line.rsplit(' ', 1)
             vmname = vmname.strip('"')

tests/modules/virtualbox/test_virtualbox_manager.py

@@ -75,9 +75,9 @@ def test_get_list(manager, loop):
     vm_list = ['"Windows 8.1" {27b4d095-ff5f-4ac4-bb9d-5f2c7861c1f1}',
                '"Carriage',
                'Return" {27b4d095-ff5f-4ac4-bb9d-5f2c7861c1f1}',
+               '',
                '"<inaccessible>" {42b4d095-ff5f-4ac4-bb9d-5f2c7861c1f1}',
-               '"Linux Microcore 4.7.1" {ccd8c50b-c172-457d-99fa-dd69371ede0e}'
-              ]
+               '"Linux Microcore 4.7.1" {ccd8c50b-c172-457d-99fa-dd69371ede0e}']
 
     @asyncio.coroutine
     def execute_mock(cmd, args):