Fix: Remove panic-in-panic failure when running tests

Symptom:

```
thread panicked while processing panic. aborting.
```

It seems to be a MPSC channel hangup problem, where the
reciever does not exist any more when transmitting value
through channel.

Root cause is not fully understood but a guess is that we
get some kind of race condition between multiple test cases
setting and resetting the `catch_panic` functionality.

Please Note! Since `std::panic::set_hook` is global, we might have
a race condition when multiple threads are running tests in
parallel. In that case, panics from other threads might interfere
with each other in the custom hook. Leaving aa-is for now.

Author: jockbert

README.md

@@ -72,6 +72,13 @@ Other known limitations:
   only try candidates within the given range `10.0..100.0`, but can also try other
   values like -10.0 and will ultimately try to shrink toward zero.
 
+* Monkey test uses the global panic hook to catch panics in code under test and
+  this can interfere with other code that also modifies the panic hook during
+  testing.
+  Since the panic hook is a global resource, it migth also have unintended
+  effects in multithreaded testing due to limitations in the current panic hook
+  handling in Monkey Test.
+
 For details on recent changes, see the [CHANGELOG](CHANGELOG.md).
 
 ## Key design principles

src/config.rs

@@ -255,6 +255,11 @@ where
     E: std::fmt::Debug + std::panic::UnwindSafe + Clone + 'static,
     P: std::panic::RefUnwindSafe + Fn(E) -> Result<(), String>,
 {
+    // Please Note! Since `std::panic::set_hook` is global, we might have a race
+    // condition here if multiple threads are running tests in parallel. In that
+    // case, panics from other threads might be caught here and hooks might
+    // interfere with each other. Leaving as-is for now.
+
     move |example: E| {
         let original_panic_hook = std::panic::take_hook();
         let (tx, rx) = mpsc::channel();
@@ -266,7 +271,10 @@ where
             if let Some(loc) = info.location() {
                 let location_text =
                     format! {"in file '{}' at line {}", loc.file(), loc.line()};
-                tx.send(location_text).unwrap();
+
+                // Ignoring send errors, since there is nothing to do if
+                // receiver has hung up. We are then out of test scope anyway.
+                let _ = tx.send(location_text);
             }
         }));