ICU-13415 Adding virtual destructor to internal Interface-like type SymbolProvider.

X-SVN-Rev: 40624

icu4c/source/i18n/number_affixutils.h

@@ -49,6 +49,8 @@ struct AffixTag {
 // Exported as U_I18N_API because it is a base class for other exported types
 class U_I18N_API SymbolProvider {
   public:
+    virtual ~SymbolProvider() = default;
+
     // TODO: Could this be more efficient if it returned by reference?
     virtual UnicodeString getSymbol(AffixPatternType type) const = 0;
 };