[doxygen] Fix crash on unclosed HTML tag

Fixes #1935

CHANGES.current

@@ -7,6 +7,10 @@ the issue number to the end of the URL: https://github.com/swig/swig/issues/
 Version 4.1.0 (in progress)
 ===========================
 
+2022-01-26: olly
+	    #1935 Don't crash on an unclosed HTML tag in a doxygen comment
+	    when -doxygen is specified.
+
 2022-01-25: olly
 	    Constant expressions now support member access with `.` such as
 	    `foo.bar`.  Previous this only worked in a case like `x->foo.bar`.

Examples/test-suite/errors/doxygen_unclosed_tag.i

@@ -0,0 +1,6 @@
+%module xxx
+
+/**
+ * Return a random variate with uniform distribution in the range [a,b), where a<b
+ */
+double uniform(double a, double b);

Examples/test-suite/errors/doxygen_unclosed_tag.stderr

@@ -0,0 +1 @@
+doxygen_unclosed_tag.i:4: Warning 563: Doxygen HTML error for tag b: HTML tag without '>' found.

Source/Doxygen/doxyparser.cxx

@@ -1241,6 +1241,9 @@ void DoxygenParser::processHtmlTags(size_t &pos, const std::string &line) {
   // prepend '<' to distinguish HTML tags from doxygen commands
   if (!cmd.empty() && addDoxyCommand(m_tokenList, '<' + cmd)) {
     // it is a valid HTML command
+    if (pos == string::npos) {
+      pos = line.size();
+    }
     if (line[pos] != '>') {
       // it should be HTML tag with args,
       // for example <A ...>, <IMG ...>, ...
@@ -1266,7 +1269,7 @@ void DoxygenParser::processHtmlTags(size_t &pos, const std::string &line) {
       }
     }
 
-    if (pos != string::npos) {
+    if (pos < line.size()) {
       pos++; // skip '>'
     }
   } else {