Fix crash with scaletool

For some reason we sometimes get an empty string. This shouldn't crash
the application.

Fixes sentry crashes:
CURA-4CC
CURA-4TE
CURA-56J

plugins/Tools/ScaleTool/ScaleTool.py

@@ -331,7 +331,11 @@ def setObjectWidth(self, width):
 
         obj = Selection.getSelectedObject(0)
         if obj:
-            width = float(width)
+            try:
+                width = float(width)
+            except ValueError:
+                Logger.warning("Unable to set width")
+                return
             obj_width = obj.getBoundingBox().width
             if not Float.fuzzyCompare(obj_width, width, DIMENSION_TOLERANCE):
                 scale_factor = width / obj_width
@@ -341,6 +345,7 @@ def setObjectWidth(self, width):
                     scale_vector = Vector(scale_factor, scale_factor, scale_factor)
 
                 self._scaleSelectedNodes(scale_vector)
+
     def setObjectHeight(self, height):
         """Set the height of the selected object(s) by scaling the first selected object to a certain height
 
@@ -349,7 +354,11 @@ def setObjectHeight(self, height):
 
         obj = Selection.getSelectedObject(0)
         if obj:
-            height = float(height)
+            try:
+                height = float(height)
+            except ValueError:
+                Logger.warning("Unable to set height")
+                return
             obj_height = obj.getBoundingBox().height
             if not Float.fuzzyCompare(obj_height, height, DIMENSION_TOLERANCE):
                 scale_factor = height / obj_height
@@ -368,7 +377,11 @@ def setObjectDepth(self, depth):
 
         obj = Selection.getSelectedObject(0)
         if obj:
-            depth = float(depth)
+            try:
+                depth = float(depth)
+            except ValueError:
+                Logger.warning("Unable to set depth")
+                return
             obj_depth = obj.getBoundingBox().depth
             if not Float.fuzzyCompare(obj_depth, depth, DIMENSION_TOLERANCE):
                 scale_factor = depth / obj_depth