Prevent mpl_PyFile_Dup from failing when given BytesIO or similar

src/_backend_agg.cpp

@@ -2168,6 +2168,7 @@ RendererAgg::write_rgba(const Py::Tuple& args)
     }
     else
     {
+        PyErr_Clear();
         PyObject* write_method = PyObject_GetAttrString(py_fileobj.ptr(),
                                                         "write");
         if (!(write_method && PyCallable_Check(write_method)))

src/file_compat.h

@@ -101,8 +101,8 @@ mpl_PyFile_Dup(PyObject *file, char *mode, mpl_off_t *orig_pos)
     /* Record the original raw file handle position */
     *orig_pos = npy_ftell(handle);
     if (*orig_pos == -1) {
-        PyErr_SetString(PyExc_IOError, "obtaining file position failed");
-        return NULL;
+        // handle is a stream, so we don't have to worry about this
+        return handle;
     }
 
     /* Seek raw handle to the Python-side position */
@@ -145,20 +145,17 @@ mpl_PyFile_DupClose(PyObject *file, FILE* handle, mpl_off_t orig_pos)
     if (fd == -1) {
         return -1;
     }
-    if (npy_lseek(fd, orig_pos, SEEK_SET) == -1) {
-        PyErr_SetString(PyExc_IOError, "seeking file failed");
-        return -1;
-    }
-
-    if (position == -1) {
-        PyErr_SetString(PyExc_IOError, "obtaining file position failed");
-        return -1;
-    }
-
-    /* Seek Python-side handle to the FILE* handle position */
-    ret = PyObject_CallMethod(file, "seek", MPL_OFF_T_PYFMT "i", position, 0);
-    if (ret == NULL) {
-        return -1;
+    if (npy_lseek(fd, orig_pos, SEEK_SET) != -1) {
+        if (position == -1) {
+            PyErr_SetString(PyExc_IOError, "obtaining file position failed");
+            return -1;
+        }
+
+        /* Seek Python-side handle to the FILE* handle position */
+        ret = PyObject_CallMethod(file, "seek", MPL_OFF_T_PYFMT "i", position, 0);
+        if (ret == NULL) {
+            return -1;
+        }
     }
     Py_DECREF(ret);
     return 0;