Check for valid identifier in WhenStmt::Describe

testing/btest/language/when-local-function-capture-error.zeek

@@ -0,0 +1,17 @@
+# @TEST-DOC: Tests that a capture in a function that doesn't exist doesn't crash
+# @TEST-EXEC-FAIL: zeek -b %INPUT >out 2>&1
+# @TeST-EXEC: TEST_DIFF_CANONIFIER=$SCRIPTS/diff-remove-abspath btest-diff out
+
+function f() {
+        local x = 1;
+        local y = 2;
+
+        when [x, z] ( T == T )
+                {
+                print "hmm?", x, y;
+                }
+        timeout 100msec
+                {
+                print "timeout";
+                }
+}