Don't crash if type is not available in Python Doxygen code

Fix crash if "@return" Doxygen tag was used on a node without any return
type (such as a class, for example). Ignoring it might not be the best
thing to do, but it's definitely better than crashing and it's not
really clear what else could be done anyhow.

Closes #1516.

Examples/test-suite/java/doxygen_misc_constructs_runme.java

@@ -117,6 +117,9 @@ public class doxygen_misc_constructs_runme {
     wantedComments.put("doxygen_misc_constructs.ClassWithNestedEnum.ENested.THREE",
     		" desc of three\n");
 
+    wantedComments.put("doxygen_misc_constructs.StructWithReturnComment",
+    		" @return This is a bad place for this tag, but it should be ignored.");
+
     wantedComments.put("doxygen_misc_constructs.doxygen_misc_constructs.showList()",
 "         An example of a list in a documentation comment.<br>\n" +
 " <br>\n" +