Fix regression in EcdsaKeyPair::from_private_key_der #208

Job	Run time
GCC 4.8 - CMake 0 - FIPS 0	5m 35s
GCC 7 - CMake 0 - FIPS 0	4m 12s
GCC 4.8 - CMake 0 - FIPS 1	7m 6s
C-std ubuntu-latest - 11 - Force CMake 0	1m 45s
GCC 7 - CMake 0 - FIPS 1	5m 42s
GCC 5 - CMake 0 - FIPS 0	5m 55s
GCC 8 - CMake 0 - FIPS 0	3m 56s
C-std ubuntu-latest - 11 - Force CMake 1	2m 2s
GCC 5 - CMake 0 - FIPS 1	7m 20s
GCC 8 - CMake 0 - FIPS 1	5m 45s
C-std ubuntu-latest - 99 - Force CMake 0	1m 33s
GCC 6 - CMake 0 - FIPS 0	5m 58s
GCC 6 - CMake 0 - FIPS 1	6m 58s
GCC 7 - CMake 1 - FIPS 0	4m 23s
C-std ubuntu-latest - 99 - Force CMake 1	1m 39s
C-std macos-13 - 11 - Force CMake 0	2m 10s
GCC 4.8 - CMake 1 - FIPS 0	5m 34s
C-std macos-13 - 11 - Force CMake 1	2m 3s
GCC 7 - CMake 1 - FIPS 1	5m 14s
GCC 4.8 - CMake 1 - FIPS 1	7m 24s
GCC 8 - CMake 1 - FIPS 0	4m 23s
C-std macos-13 - 99 - Force CMake 0	3m 6s
GCC 5 - CMake 1 - FIPS 0	5m 35s
C-std macos-13 - 99 - Force CMake 1	2m 22s
GCC 5 - CMake 1 - FIPS 1	7m 17s
C-std macos-14-xlarge - 11 - Force CMake 0	1m 34s
GCC 6 - CMake 1 - FIPS 0	5m 34s
C-std macos-14-xlarge - 11 - Force CMake 1	1m 20s
GCC 6 - CMake 1 - FIPS 1	7m 31s
GCC 8 - CMake 1 - FIPS 1	5m 13s
C-std macos-14-xlarge - 99 - Force CMake 0	1m 28s
C-std macos-14-xlarge - 99 - Force CMake 1	1m 22s
C-std windows-latest - 11 - Force CMake 0	3m 26s
C-std windows-latest - 11 - Force CMake 1	3m 45s
C-std windows-latest - 99 - Force CMake 0	3m 56s
C-std windows-latest - 99 - Force CMake 1	3m 41s
	2h 33m 47s

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