Test clearing out-of-bounds bits with ASN1_BIT_STRING_set_bit

I was doing some experiments, had a bug in this case, and our tests
didn't notice.

Bug: 42290311
Change-Id: I3bf8e9dec2abac455ef59c4cb809ec10af370243
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/86127
Auto-Submit: David Benjamin <davidben@google.com>
Reviewed-by: Lily Chen <chlily@google.com>
Commit-Queue: Lily Chen <chlily@google.com>

crypto/asn1/asn1_test.cc

diff --git a/crypto/asn1/asn1_test.cc b/crypto/asn1/asn1_test.cc
index dced405..e93e356 100644
--- a/crypto/asn1/asn1_test.cc
+++ b/crypto/asn1/asn1_test.cc
@@ -889,6 +889,11 @@
   EXPECT_EQ(0, ASN1_BIT_STRING_get_bit(val.get(), 3));
   EXPECT_EQ(0, ASN1_BIT_STRING_get_bit(val.get(), 4));
 
+  // Bits that were already out-of-bounds and clear may be cleared. This is a
+  // no-op.
+  ASSERT_TRUE(ASN1_BIT_STRING_set_bit(val.get(), 100, 0));
+  TestSerialize(val.get(), i2d_ASN1_BIT_STRING, kBitString1);
+
   // Bits may be set beyond the end of the string.
   ASSERT_TRUE(ASN1_BIT_STRING_set_bit(val.get(), 63, 1));
   static const uint8_t kBitStringLong[] = {0x03, 0x09, 0x00, 0x80, 0x00, 0x00,