Merge #16995: Fix gcc 9 warnings

ff9c671b11d40e5d0623eff3dd12e48cbaafb34e refactor: Work around GCC 9 `-Wredundant-move` warning (Russell Yanofsky)
b837b334db5dd6232725fd2350928ff4fbd3feee net: Fail instead of truncate command name in CMessageHeader (Wladimir J. van der Laan)

Pull request description:

  Fixes all 3 from #16992 (see commits)

  - net: Fail instead of truncate command name in CMessageHeader
  - refactor: Use std::move workaround for unique_ptr upcast only when necessary

ACKs for top commit:
  practicalswift:
    ACK ff9c671b11d40e5d0623eff3dd12e48cbaafb34e -- patch looks correct
  sipa:
    utACK ff9c671b11d40e5d0623eff3dd12e48cbaafb34e
  ryanofsky:
    Code review ACK ff9c671b11d40e5d0623eff3dd12e48cbaafb34e. Looks good and seems to pass travis, modulo a timeout on one build
  hebasto:
    ACK ff9c671b11d40e5d0623eff3dd12e48cbaafb34e, tested on Fedora 31:

Tree-SHA512: 52d8c13aaf0d56f9bc546a98d7f853eae21f7e325b202fdeb2286b19a9a0ee308634c644b039f60ad8043421e382381cbf1bce58d9f807547f928621c7d245d0

1 files changed, 4 insertions, 5 deletions

diff --git a/src/interfaces/chain.cpp b/src/interfaces/chain.cpp
index 9dc0d37cd9..775a89f4cf 100644
--- a/src/interfaces/chain.cpp
+++ b/src/interfaces/chain.cpp
@@ -234,11 +234,10 @@ public:
     explicit ChainImpl(NodeContext& node) : m_node(node) {}
     std::unique_ptr<Chain::Lock> lock(bool try_lock) override
     {
-        auto result = MakeUnique<LockImpl>(::cs_main, "cs_main", __FILE__, __LINE__, try_lock);
-        if (try_lock && result && !*result) return {};
-        // std::move necessary on some compilers due to conversion from
-        // LockImpl to Lock pointer
-        return std::move(result);
+        auto lock = MakeUnique<LockImpl>(::cs_main, "cs_main", __FILE__, __LINE__, try_lock);
+        if (try_lock && lock && !*lock) return {};
+        std::unique_ptr<Chain::Lock> result = std::move(lock); // Temporary to avoid CWG 1579
+        return result;
     }
     bool findBlock(const uint256& hash, CBlock* block, int64_t* time, int64_t* time_max) override
     {