Initialize fallback command tag for CompileFunctionStmt

`CreateCommandTag()` can leave `tag` uninitialized for
`CompileFunctionStmt` when objtype is neither FUNCTION nor PROCEDURE.
Callers normally pass one of those two values, but Clang still reports
the missing fallback path.

Warning excerpt:

```
utility.c:2757:13: warning: variable 'tag' is used uninitialized whenever 'if' condition is false
[-Wsometimes-uninitialized]
```

Set `tag = CMDTAG_UNKNOWN` in the remaining branch so the fallback
behavior is explicit.

Author: c2main

src/backend/tcop/utility.c

@@ -2748,6 +2748,8 @@ CreateCommandTag(Node *parsetree)
 				tag = CMDTAG_ALTER_PROCEDURE;
 			else if (((CompileFunctionStmt *) parsetree)->objtype == OBJECT_FUNCTION)
 				tag = CMDTAG_ALTER_FUNCTION;
+			else
+				tag = CMDTAG_UNKNOWN;
 			break;
 
 		case T_GrantStmt: