Fix overzealous CHECK in custom EC_KEYs.

If any EC_KEY with EX_DATA is duplicated, whether or not it is one of ours,
ExDataDup may get called. This is unlikely to ever happen (I don't think
we ever dup any EC_KEY on the client, and dup_ex_data has a fast-path if
the EX_DATA has never been touched anyway), but the CHECK is a little
overzealous.

BUG=none

Review URL: https://codereview.chromium.org/506813002

Cr-Commit-Position: refs/heads/master@{#292210}

net/android/keystore_openssl.cc

@@ -92,7 +92,7 @@ int ExDataDup(CRYPTO_EX_DATA* to,
               int index,
               long argl,
               void* argp) {
-  CHECK(false);
+  CHECK_EQ((void*)NULL, *from_d);
   return 0;
 }
 

net/ssl/openssl_platform_key_mac.cc

@@ -107,7 +107,7 @@ int ExDataDup(CRYPTO_EX_DATA* to,
               int idx,
               long argl,
               void* argp) {
-  CHECK(false);
+  CHECK_EQ((void*)NULL, *from_d);
   return 0;
 }