fix(parser): diagnose GLOBL and DATA without a symbol name

A bare GLOBL or DATA parsed without a single diagnostic while leaving a
nil Name in the tree, a pointer every downstream tool dereferences; TEXT
keeps a placeholder beside its error for exactly that reason, and GLOBL
and DATA now do the same.  The crashing input enters the corpus.

Assisted-by: GLM 5.3

parser/parser.go

@@ -299,6 +299,13 @@ func (p *state) parseGlobl(line []token.Token) *ast.Globl {
 	g := &ast.Globl{Keyword: line[0]}
 	rest := skipComma(line[1:])
 	sym, n := parseSymbolPrefix(rest)
+	if sym == nil {
+		// A usable tree without a name cannot be had, and the linter and LSP
+		// dereference Name on every parsed GLOBL, so the decl keeps a
+		// placeholder beside its error, exactly as TEXT does.
+		p.errorf(line[0].Pos, "GLOBL missing a symbol name")
+		sym = &ast.Symbol{Pos: line[0].Pos, Raw: "?", Name: "?"}
+	}
 	g.Name = sym
 	rest = skipComma(rest[n:])
 	// Flags are identifiers (RODATA, DUPOK) or legacy numeric constants
@@ -324,6 +331,12 @@ func (p *state) parseData(line []token.Token) *ast.Data {
 	nameGroup, valuePart := splitFirstComma(rest)
 	nameGroup, width := splitTrailingWidth(nameGroup)
 	sym, _ := parseSymbolPrefix(nameGroup)
+	if sym == nil {
+		// Same contract as TEXT and GLOBL: the tree stays usable beside its
+		// error, because downstream tools dereference Name unconditionally.
+		p.errorf(line[0].Pos, "DATA missing a symbol name")
+		sym = &ast.Symbol{Pos: line[0].Pos, Raw: "?", Name: "?"}
+	}
 	d.Name = sym
 	d.Width = width
 	if len(valuePart) > 0 {