Improve macOS pthread detection exception handling

This commit adds the pthread library loading exception to
the logger and assumes that the current thread is the main
thread if no pthread library is found.

src/imagej/__init__.py

@@ -1530,10 +1530,13 @@ def _macos_is_main_thread():
     # try to load the pthread library
     try:
         pthread = cdll.LoadLibrary("libpthread.dylib")
-    except OSError as e:
-        print("No pthread library found.", e)
+    except OSError as exc:
+        _log_exception(_logger, exc)
+        print("No pthread library found.")
+        # assume the current thread is the main thread
+        return True
 
-    # detect if main thread
+    # detect if the current thread is the main thread
     if pthread.pthread_main_np() == 1:
         return True
     else: