Test image.width and image.height without using 'is not None'

- Simplification requested by @formatc1702 in review of #153
- Inspection of size_html_cell() in Graphviz source code
  https://gitlab.com/graphviz/graphviz/-/blob/master/lib/common/htmltable.c#L1210-1221
  supports that a zero value is treated as not specified.

src/wireviz/DataClasses.py

@@ -16,23 +16,25 @@ class Image:
     width: Optional[int] = None
     height: Optional[int] = None
     fixedsize: Optional[bool] = None
-    # Contents of the cell <td> just below the image cell:
+    # Contents of the text cell <td> just below the image cell:
     caption: Optional[str] = None
     # See also HTML doc at https://graphviz.org/doc/info/shapes.html#html
 
     def __post_init__(self):
 
         if self.scale is None:
-            self.scale = "false" if self.width is None     and self.height is None \
+            self.scale = "false" if not self.width and not self.height \
-                else     "both"  if self.width is not None and self.height is not None \
+                else     "both"  if     self.width and     self.height \
                 else     "true" # When only one dimension is specified.
 
         if self.fixedsize is None:
-            self.fixedsize = self.width is not None or self.height is not None
+            self.fixedsize = self.width or self.height
 
-        if self.width is None and self.height is not None:
+        if self.height:
+            if not self.width:
                 self.width = self.height # Assuming 1:1 aspect ratio for now.
-        elif self.height is None and self.width is not None:
+        else:
+            if self.width:
                 self.height = self.width # Assuming 1:1 aspect ratio for now.
 
 

src/wireviz/wv_helper.py

@@ -75,8 +75,8 @@ def html_caption(image):
 
 def html_size_attr(image):
     # Return Graphviz HTML attributes to specify minimum or fixed size of a TABLE or TD object
-    return ((f' width="{image.width}"'   if image.width is not None else '')
+    return ((f' width="{image.width}"'   if image.width else '')
-        +   (f' height="{image.height}"' if image.height is not None else '')
+        +   (f' height="{image.height}"' if image.height else '')
         +   ( ' fixedsize="true"'        if image.fixedsize else '')) if image else ''