Fix for uninitialized field (shader-slang#1838)

The `OverloadedExpr` type didn't provide a default value for its field:

    Name* name;

This led to a null-pointer crash in the logic that deals with synthesizing interface requirements because it creates an `OverloadedExpr` but doesn't initialize the field.

This change makes two fixes:

1. The logic in the synthesis path actually initializes `name` so that it can feed into any downstream error messages

2. The `OverloadedExpr` declaration now includes an initial value for `name` so that it will at least be null instead of garbage if we slip up again

Author: Tim Foley

source/slang/slang-ast-expr.h

@@ -35,7 +35,7 @@ class OverloadedExpr : public Expr
     SLANG_AST_CLASS(OverloadedExpr)
 
     // The name that was looked up and found to be overloaded
-    Name* name;
+    Name* name = nullptr;
 
     // Optional: the base expression is this overloaded result
     // arose from a member-reference expression.

source/slang/slang-check-decl.cpp

@@ -2062,6 +2062,7 @@ namespace Slang
         // expression.
         //
         auto synBase = m_astBuilder->create<OverloadedExpr>();
+        synBase->name = requiredMemberDeclRef.getDecl()->getName();
         synBase->lookupResult2 = lookupResult;
 
         // If `synThis` is non-null, then we will use it as the base of