Fix unused local scope codegen

[gshaowei6]

Fixes #96.

BlockWriter previously threw CodeGenException: outOfScope... when javac emitted a store for an unused local at the end of a scope but omitted the corresponding LocalVariableTable entry. In that case the bytecode still contains the RHS expression, but there is no recoverable local name/type to declare in generated OpenCL.

This patch preserves the RHS expression for any potential side effects and suppresses the unrecoverable local assignment instead of throwing. It also enables the ignored ArbitraryScopeTest and updates NonNullCheckTest, which is the same unused-local-at-end-of-scope pattern.

Tests:

• RED: after removing @Ignore from ArbitraryScopeTest, mvn "-Dtest=com.aparapi.codegen.test.ArbitraryScopeTest" test failed with CodeGenException: outOfScope193 = before the fix.
• mvn "-Dtest=com.aparapi.codegen.test.ArbitraryScopeTest,com.aparapi.codegen.test.NonNullCheckTest,com.aparapi.codegen.test.NullCheckTest,com.aparapi.codegen.test.ArbitraryScopeSimpleTest,com.aparapi.codegen.test.ArbitraryScope2Test" test (10 tests, 0 failures)
• mvn "-Dtest=com.aparapi.codegen.test.*Test" test completed; target/surefire-reports contains 434 tests, 0 failures, 0 errors, 2 skipped
• git diff --check