idl: fix out of bounds string accesses

Change-Id: Id0d07ff9bcd4858cb74458eaf13fb9386387f455

idl/inc/lex.hxx

@@ -140,7 +140,9 @@ class SvTokenStream
     int             GetNextChar();
     int             GetFastNextChar()
                     {
-                        return aBufStr[nBufPos++];
+                        return (nBufPos < aBufStr.getLength())
+                            ? aBufStr[nBufPos++]
+                            : '\0';
                     }
 
     void            FillTokenList();

idl/source/cmptools/lex.cxx

@@ -151,9 +151,9 @@ void SvTokenStream::FillTokenList()
 int SvTokenStream::GetNextChar()
 {
     int nChar;
-    if( aBufStr.getLength() < nBufPos )
+    while (aBufStr.getLength() <= nBufPos)
     {
-        if( rInStream.ReadLine( aBufStr ) )
+        if (rInStream.ReadLine(aBufStr))
         {
             nLine++;
             nColumn = 0;