Re-create the Context in InitDecoder if it is null.

The context may have been destroyed because it was lost, recreate it for
the next iteration of the fuzzer.

BUG=907303
BUG=907350

Change-Id: Ie2acb7d8da68be7f96427766c697624e0d54bd7a
Reviewed-on: https://chromium-review.googlesource.com/c/1346730
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Antoine Labour <piman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#610179}

gpu/command_buffer/tests/fuzzer_main.cc

@@ -335,7 +335,7 @@ class CommandBufferSetup {
   }
 
   bool InitDecoder() {
-    if (recreate_context_) {
+    if (!context_) {
       InitContext();
     }