Fix segfault in Python 3.12b4 (#238)

In `flo_read` and `flo_write` there were calls to `Py_DECREF` after releasing the GIL.

Closes #237

yara-python.c

@@ -1394,10 +1394,12 @@ static size_t flo_read(
     PyObject* bytes = PyObject_CallMethod(
         (PyObject*) user_data, "read", "n", (Py_ssize_t) size);
 
+    if (bytes == NULL) 
+    {
       PyGILState_Release(gil_state);
+      return i;
+    }
 
-    if (bytes != NULL)
-    {
     Py_ssize_t len;
     char* buffer;
 
@@ -1406,17 +1408,14 @@ static size_t flo_read(
     if (result == -1 || (size_t) len < size)
     {
       Py_DECREF(bytes);
+      PyGILState_Release(gil_state);
       return i;
     }
 
     memcpy((char*) ptr + i * size, buffer, size);
 
     Py_DECREF(bytes);
-    }
-    else
-    {
-      return i;
-    }
+    PyGILState_Release(gil_state);
   }
 
   return count;
@@ -1444,12 +1443,11 @@ static size_t flo_write(
         (PyObject*) user_data, "write", "s#", (char*) ptr + i * size, size);
     #endif
 
+    Py_XDECREF(result);
     PyGILState_Release(gil_state);
 
     if (result == NULL)
       return i;
-
-    Py_DECREF(result);
   }
 
   return count;