starmath: Return SmGlyphSpecialNode from DoGlyphSpecial()

instead of pushing it to the stack. This spares some pops.

Change-Id: I9fc987ebf851ff6387e347a2878ff01f482d8f7f
Reviewed-on: https://gerrit.libreoffice.org/35029Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Takeshi Abe <tabe@fixedpoint.jp>

starmath/inc/parse.hxx

@@ -89,7 +89,7 @@ class SmParser
     void    DoStack();
     void    DoMatrix();
     void    DoSpecial();
-    void    DoGlyphSpecial();
+    SmGlyphSpecialNode *DoGlyphSpecial();
     // end of grammar
 
     void    Error(SmParseError Error);

starmath/source/parse.cxx

@@ -1124,9 +1124,7 @@ void SmParser::DoProduct()
                 //Let the glyph node know it's a binary operation
                 m_aCurToken.eType = TBOPER;
                 m_aCurToken.nGroup = TG::Product;
-
-                DoGlyphSpecial();
-                pOper = popOrZero(m_aNodeStack);
+                pOper = DoGlyphSpecial();
                 break;
 
             case TOVERBRACE :
@@ -1660,8 +1658,7 @@ void SmParser::DoUnOper()
             //Let the glyph know what it is...
             m_aCurToken.eType = TUOPER;
             m_aCurToken.nGroup = TG::UnOper;
-            DoGlyphSpecial();
-            pOper = popOrZero(m_aNodeStack);
+            pOper = DoGlyphSpecial();
             break;
 
         case TPLUS :
@@ -2253,10 +2250,11 @@ void SmParser::DoSpecial()
     NextToken();
 }
 
-void SmParser::DoGlyphSpecial()
+SmGlyphSpecialNode *SmParser::DoGlyphSpecial()
 {
-    m_aNodeStack.push_front(o3tl::make_unique<SmGlyphSpecialNode>(m_aCurToken));
+    auto pNode = o3tl::make_unique<SmGlyphSpecialNode>(m_aCurToken);
     NextToken();
+    return pNode.release();
 }
 
 void SmParser::Error(SmParseError eError)