Add missing virtual destructors to all helper classes

include/qpdf/QPDFAcroFormDocumentHelper.hh

@@ -85,6 +85,10 @@ class QPDFAcroFormDocumentHelper: public QPDFDocumentHelper
   public:
     QPDF_DLL
     QPDFAcroFormDocumentHelper(QPDF&);
+    QPDF_DLL
+    virtual ~QPDFAcroFormDocumentHelper()
+    {
+    }
 
     // This class lazily creates an internal cache of the mapping
     // among form fields, annotations, and pages. Methods within this

include/qpdf/QPDFAnnotationObjectHelper.hh

@@ -31,6 +31,10 @@ class QPDFAnnotationObjectHelper: public QPDFObjectHelper
   public:
     QPDF_DLL
     QPDFAnnotationObjectHelper(QPDFObjectHandle);
+    QPDF_DLL
+    virtual ~QPDFAnnotationObjectHelper()
+    {
+    }
 
     // This class provides helper methods for certain types of
     // annotations. At its introduction, it only supports Widget

include/qpdf/QPDFFormFieldObjectHelper.hh

@@ -37,6 +37,10 @@ class QPDFFormFieldObjectHelper: public QPDFObjectHelper
     QPDFFormFieldObjectHelper();
     QPDF_DLL
     QPDFFormFieldObjectHelper(QPDFObjectHandle);
+    QPDF_DLL
+    virtual ~QPDFFormFieldObjectHelper()
+    {
+    }
 
     QPDF_DLL
     bool isNull();

include/qpdf/QPDFNumberTreeObjectHelper.hh

@@ -41,6 +41,10 @@ class QPDFNumberTreeObjectHelper: public QPDFObjectHelper
   public:
     QPDF_DLL
     QPDFNumberTreeObjectHelper(QPDFObjectHandle);
+    QPDF_DLL
+    virtual ~QPDFNumberTreeObjectHelper()
+    {
+    }
 
     typedef long long int numtree_number;
 

include/qpdf/QPDFPageDocumentHelper.hh

@@ -36,6 +36,10 @@ class QPDFPageDocumentHelper: public QPDFDocumentHelper
   public:
     QPDF_DLL
     QPDFPageDocumentHelper(QPDF&);
+    QPDF_DLL
+    virtual ~QPDFPageDocumentHelper()
+    {
+    }
 
     // Traverse page tree, and return all /Page objects wrapped in
     // QPDFPageObjectHelper objects. Unlike with

include/qpdf/QPDFPageLabelDocumentHelper.hh

@@ -49,6 +49,10 @@ class QPDFPageLabelDocumentHelper: public QPDFDocumentHelper
   public:
     QPDF_DLL
     QPDFPageLabelDocumentHelper(QPDF&);
+    QPDF_DLL
+    virtual ~QPDFPageLabelDocumentHelper()
+    {
+    }
 
     QPDF_DLL
     bool hasPageLabels();

include/qpdf/QPDFPageObjectHelper.hh

@@ -34,6 +34,10 @@ class QPDFPageObjectHelper: public QPDFObjectHelper
   public:
     QPDF_DLL
     QPDFPageObjectHelper(QPDFObjectHandle);
+    QPDF_DLL
+    virtual ~QPDFPageObjectHelper()
+    {
+    }
 
     // Returns an empty map if there are no images or no resources.
     // This function does not presently support inherited resources.