Make some (do-nothing) destructors in the chardet library virtual, should fix some warnings on some GCC versions.

Originally committed to SVN as r3403.

aegisub/universalchardet/CharDistribution.h

@@ -46,6 +46,7 @@ class CharDistributionAnalysis
 {
 public:
   CharDistributionAnalysis() {Reset();};
+  virtual ~CharDistributionAnalysis() {};
 
   //feed a block of data and do distribution analysis
   void HandleData(const char* aBuf, PRUint32 aLen) {};

aegisub/universalchardet/JpCntx.h

@@ -52,6 +52,7 @@ class JapaneseContextAnalysis
 {
 public:
   JapaneseContextAnalysis() {Reset();};
+  virtual ~JapaneseContextAnalysis() {};
 
   void HandleData(const char* aBuf, PRUint32 aLen);