Fix TestMultithreaded when there's no debugserver specified

r325858 was bogus and would error out with a KeyError when --server
was not passed to dotest.py.

llvm-svn: 325862

lldb/packages/Python/lldbsuite/test/api/multithreaded/TestMultithreaded.py

@@ -101,7 +101,7 @@ class SBBreakpointCallbackCase(TestBase):
         exe = [test_exe, self.getBuildArtifact(self.inferior)]
 
         env = {self.dylibPath: self.getLLDBLibraryEnvVal()}
-        if os.environ['LLDB_DEBUGSERVER_PATH']:
+        if 'LLDB_DEBUGSERVER_PATH' in os.environ:
             env['LLDB_DEBUGSERVER_PATH'] = os.environ['LLDB_DEBUGSERVER_PATH']
         if self.TraceOn():
             print("Running test %s" % " ".join(exe))