Merge bitcoin#30026: refactor, test: Always initialize pointer

bd2de7a refactor, test: Always initialize pointer (Hennadii Stepanov)

Pull request description:

  This change fixes MSVC warning [C4703](https://learn.microsoft.com/en-us/cpp/error-messages/compiler-warnings/compiler-warning-level-4-c4703).

  All `DisableSpecificWarnings` dropped from `test_bitcoin.vcxproj` as all remained are inherited from `common.init.vcxproj`.

  Required to simplify warning suppression porting to the CMake-based build system.

ACKs for top commit:
  maflcko:
    utACK bd2de7a
  sipsorcery:
    utACK bd2de7a.
  ryanofsky:
    Code review ACK bd2de7a

Tree-SHA512: 006db041d3c3697a77d9df14de86cf7c8a10804b45789df01268b2236cf6452e77dc57e89f5d5a6bc26d4b5cd483f0722d6035649c8a523b57954bb1fc810d0c

build_msvc/test_bitcoin/test_bitcoin.vcxproj

@@ -59,11 +59,6 @@
       <Project>{18430fef-6b61-4c53-b396-718e02850f1b}</Project>
     </ProjectReference>
   </ItemGroup>
-  <ItemDefinitionGroup>
-     <ClCompile>
-       <DisableSpecificWarnings>4018;4244;4267;4703;4715;4805</DisableSpecificWarnings>
-     </ClCompile>
-  </ItemDefinitionGroup>
   <Target Name="RawBenchHeaderGen" BeforeTargets="PrepareForBuild">
     <PropertyGroup>
       <ErrorText>There was an error executing the JSON test header generation task.</ErrorText>

src/test/validation_chainstate_tests.cpp

@@ -12,6 +12,7 @@
 #include <test/util/random.h>
 #include <test/util/setup_common.h>
 #include <uint256.h>
+#include <util/check.h>
 #include <validation.h>
 
 #include <vector>
@@ -102,14 +103,14 @@ BOOST_FIXTURE_TEST_CASE(chainstate_update_tip, TestChain100Setup)
 
     BOOST_CHECK_EQUAL(chainman.GetAll().size(), 2);
 
-    Chainstate& background_cs{*[&] {
+    Chainstate& background_cs{*Assert([&]() -> Chainstate* {
         for (Chainstate* cs : chainman.GetAll()) {
             if (cs != &chainman.ActiveChainstate()) {
                 return cs;
             }
         }
-        assert(false);
-    }()};
+        return nullptr;
+    }())};
 
     // Append the first block to the background chain.
     BlockValidationState state;