Fix #272: check `c_obj_create` error code for `OBJ_R_OID_EXISTS`. #330

Job	Run time
cygwin (windows-2019, win64, -DOQS_ALGS_ENABLED=STD)	6m 5s
msvc (windows-2019, win64, -DOQS_ALGS_ENABLED=STD, no-shared no-fips VC-WIN64A-masm)	59s
msvc_native (windows-2019, win64, -DOQS_ALGS_ENABLED=STD, no-shared no-fips VC-WIN64A, .CMake/too...	1s
msvc_native (windows-2022, win64, -DOQS_ALGS_ENABLED=STD, no-shared no-fips VC-WIN64A, .CMake/too...	2m 45s
	9m 50s

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