Prevent ECC tmp key leak and UB #3201

Job	Run time
make check (--enable-intelrdseed --enable-smallstackcache --enable-smallstack --enable-all CFLAGS...	2m 34s
make check (--enable-wolfEntropy --enable-smallstackcache --enable-smallstack --enable-all CFLAGS...	4m 30s
make check (--enable-amdrand --enable-smallstackcache --enable-smallstack --enable-all CFLAGS="-D...	2m 51s
make check (--enable-all --enable-debug-trace-errcodes CFLAGS="-DWC_RNG_SEED_CB -DWOLFSSL_TRACK_M...	3m 5s
make check (--enable-smallstackcache --enable-smallstack --enable-all --enable-debug-trace-errcod...	3m 5s
make check (--disable-asm --enable-wolfEntropy --enable-smallstackcache --enable-smallstack --ena...	4m 44s
make check (--enable-smallstack --enable-all CFLAGS="-DWC_RNG_SEED_CB -DWOLFSSL_TRACK_MEMORY -DW...	2m 59s
	23m 48s

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