Merge pull request matplotlib#3324 from mdboom/backend-agg-crash

BUG : fixes memory corruption issues with zero-size rasterized artists

Fix matplotlib#3304.

src/_backend_agg.cpp

@@ -2408,7 +2408,7 @@ RendererAgg::tostring_rgba_minimized(const Py::Tuple& args)
         data = PyBytes_FromStringAndSize(NULL, newsize);
         if (data == NULL)
         {
-            throw Py::MemoryError("RendererAgg::tostring_minimized could not allocate memory");
+            throw Py::MemoryError("RendererAgg::tostring_rgba_minimized could not allocate memory");
         }
         dst = (unsigned int *)PyBytes_AsString(data);
 
@@ -2420,6 +2420,12 @@ RendererAgg::tostring_rgba_minimized(const Py::Tuple& args)
                 *dst = src[y * width + x];
             }
         }
+    } else {
+        data = PyBytes_FromStringAndSize(NULL, 0);
+        if (data == NULL)
+        {
+            throw Py::MemoryError("RendererAgg::tostring_rgba_minimized could not allocate memory");
+        }
     }
 
     Py::Tuple bounds(4);
@@ -2429,8 +2435,7 @@ RendererAgg::tostring_rgba_minimized(const Py::Tuple& args)
     bounds[3] = Py::Int(newheight);
 
     Py::Tuple result(2);
-    result[0] = Py::Object(data, false);
-    Py_DECREF(data);
+    result[0] = Py::Object(data, true);
     result[1] = bounds;
 
     return result;