Fix segfault parsing varargs with -doxygen

Closes swig#1643

Author: wsfulton

CHANGES.current

@@ -7,6 +7,10 @@ the issue number to the end of the URL: https://github.com/swig/swig/issues/
 Version 4.0.2 (in progress)
 ===========================
 
+2020-01-16: mcfarljm
+            #1643 #1654 When using -doxygen, fix segfault when nameless parameters or vararg parameters
+            are used.
+
 2020-01-16: mcfarljm
             #1632 #1659 Fix newline handling for doxygen "///" comments.
 

Source/Doxygen/pydoc.cxx

@@ -449,12 +449,12 @@ std::string PyDocConverter::getParamValue(std::string param) {
   ParmList *plist = CopyParmList(Getattr(currentNode, "parms"));
   for (Parm *p = plist; p; p = nextSibling(p)) {
     String *pname = Getattr(p, "name");
-    if (Char(pname) != param)
-      continue;
-
-    String *pval = Getattr(p, "value");
-    if (pval) value = Char(pval);
-    break;
+    if (pname && Char(pname) == param) {
+      String *pval = Getattr(p, "value");
+      if (pval)
+	value = Char(pval);
+      break;
+    }
   }
   Delete(plist);
   return value;