[Sketcher] Workaround for Elements theme issue

After merging the change to the Constraint status label in 1acb74072,
the TaskSketcherElements would sometimes be reduced in size to just a
line or two, if multiple task views were expanded and a stylesheet was
enabled. This commit introduces a minimum size to the TSE to prevent
that from occurring.

src/Mod/Sketcher/Gui/TaskSketcherElements.ui

@@ -10,6 +10,12 @@
     <height>401</height>
    </rect>
   </property>
+  <property name="minimumSize">
+   <size>
+    <width>0</width>
+    <height>400</height>
+   </size>
+  </property>
   <property name="windowTitle">
    <string>Form</string>
   </property>