Fix empty fragment handling in DTLS message reassembly.

Found with libFuzzer.

Bug: chromium:763097
Change-Id: I806bcfc714c0629ff7f725e37f4c0045d4ec7ac6
Reviewed-on: https://boringssl-review.googlesource.com/20105
Commit-Queue: David Benjamin <davidben@google.com>
Commit-Queue: Steven Valdez <svaldez@google.com>
Reviewed-by: Steven Valdez <svaldez@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
diff --git a/ssl/test/runner/runner.go b/ssl/test/runner/runner.go
index 89f0713..2ffe795 100644
--- a/ssl/test/runner/runner.go
+++ b/ssl/test/runner/runner.go
@@ -2123,6 +2123,19 @@
 			},
 		},
 		{
+			testType: serverTest,
+			protocol: dtls,
+			name:     "SendEmptyFragments-Padded-DTLS",
+			config: Config{
+				Bugs: ProtocolBugs{
+					// Test empty fragments for a message with a
+					// nice power-of-two length.
+					PadClientHello:     64,
+					SendEmptyFragments: true,
+				},
+			},
+		},
+		{
 			name: "BadFinished-Client",
 			config: Config{
 				MaxVersion: VersionTLS12,