Handle fork server pipe read and write failures gracefully.

Previously it was assumed practically impossible to fail the checks. But it could happen if the binary hit I/O errors e.g. due to non-local filesystems.

PiperOrigin-RevId: 987546056

centipede/command.cc

diff --git a/centipede/command.cc b/centipede/command.cc
index 48ca89f..43100e4 100644
--- a/centipede/command.cc
+++ b/centipede/command.cc
@@ -405,11 +405,18 @@
 
     // Wake up the fork server.
     char x = ' ';
-    FUZZTEST_CHECK_EQ(1, write(fork_server_->pipe_[0], &x, 1));
+    if (write(fork_server_->pipe_[0], &x, 1) != 1) {
+      LogProblemInfo(
+          absl::StrCat("Failed to write to fork server pipe. Errno: ", errno));
+      return false;
+    }
     // Read the one-byte ack.
     // Use 60s as an arbitrary duration to wait for the process to load and
     // enter the fork server.
-    FUZZTEST_CHECK(fork_server_->ReadPipe(absl::Now() + absl::Seconds(60), x));
+    if (!fork_server_->ReadPipe(absl::Now() + absl::Seconds(60), x)) {
+      LogProblemInfo("Failed to read from fork server pipe.");
+      return false;
+    }
   } else {
     FUZZTEST_CHECK_EQ(pid_, -1);