Do not crash when Bitmap file is not found

Belonging to [master]:
  - #2714

Author: hkiel

Examples/generate_icons.py

@@ -290,12 +290,14 @@ def getGraphicsForClass(modelicaClass):
                 graphicsObj['href'] = "data:image;base64,"+g[9].strip('"')
             else:
                 fname = ask_omc('uriToFilename', g[8], parsed=False).strip().strip('"')
+                if not os.path.exists(fname):
+                    fname = os.path.join(baseDir, g[8].strip('"'))
                 if os.path.exists(fname):
                     fdata = open(fname, "rb").read()
+                    graphicsObj['href'] = "data:image;base64,"+base64.b64encode(fdata)
                 else:
-                    fname = os.path.join(baseDir, g[8].strip('"'))
-                    fdata = open(fname, "rb").read()
-                graphicsObj['href'] = "data:image;base64,"+base64.b64encode(fdata)
+                    logger.error("Could not find bitmap file {0}".format(g[8]))
+                    graphicsObj['href'] = g[8].strip('"')
 
         if not 'type' in graphicsObj:
             r = regex_any.search(icon_line)
@@ -1142,11 +1144,11 @@ def generateSvg(filename, iconGraphics, includeInvisibleText, warn_duplicates):
     hashPath = os.path.join(os.path.dirname(filename),hashName[:1],hashName)
     if not os.path.exists(hashPath):
         dwg.saveas(hashPath)
-    if not os.path.exists(filename):
+    if not os.path.islink(filename):
         try:
             os.symlink(hashName, filename)
         except OSError as e:
-            logger.error(filename + " already exists")
+            logger.error('Target file {0} already exists'.format(filename))
     else:
         if warn_duplicates:
             logger.warning('Target file {0} already exists'.format(filename))