Fix some PNG loading issues on Windows

Fix GNS3#2085

Author: julien-duponchelle

gns3/qt/qimage_svg_renderer.py

@@ -53,7 +53,7 @@ def load(self, path_or_data):
             # We load the SVG with ElementTree before
             # because Qt when failing loading send noise to logs
             # and their is no way to prevent that
-            if not path_or_data.startswith(":"):
+            if not path_or_data.startswith(":") and os.path.exists(path_or_data):
                 ET.parse(path_or_data)
             res = super().load(path_or_data)
             # If we can't render a SVG we load and base64 the image to create a SVG

tests/qt/test_qimage_svg_renderer.py

@@ -29,3 +29,13 @@ def test_render_svg():
 def test_render_png():
     renderer = QImageSvgRenderer('resources/images/gns3_icon_256x256.png')
     assert renderer.isValid()
+
+
+def test_render_text_svg():
+    renderer = QImageSvgRenderer('<svg></svg>')
+    assert renderer.isValid()
+
+
+def test_render_text_broken_svg():
+    renderer = QImageSvgRenderer('<svg></svg')
+    assert renderer.isValid() is False