BaseTools/VfrCompile/Pccts: Add virtual destructor for class DLGInputStream

Class DLGInputStream defined in DLexerBase.h has a virtual method but no
virtual destructor.

This commit add an empty virtual destructor to avoid potential
memory/resource leak when an object of a class derived from class
DLGInputStream is deleted through a pointer to the DLGInputStream class.

Cc: Liming Gao <liming.gao@intel.com>
Cc: Yonghong Zhu <yonghong.zhu@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Cc: Dandan Bi <dandan.bi@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Hao Wu <hao.a.wu@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>

BaseTools/Source/C/VfrCompile/Pccts/h/DLexerBase.h

@@ -57,6 +57,7 @@ public:
 class DllExportPCCTS DLGInputStream {
 public:
 	virtual int nextChar() = 0;
+    virtual ~DLGInputStream() {};
 };
 
 /* Predefined char stream: Input from FILE */