Fix 'make translations' run

Recent commits introduced strings in .ui files without context
which makes 'make translations' fail with:

[build POT] pot.done
Traceback (most recent call last):
  File "/home/gabor/src/core/solenv/bin/uiex", line 30, in <module>
    keyid = entry.msgctxt + '|' + entry.msgid
TypeError: unsupported operand type(s) for +: 'NoneType' and 'str'

Affected commits are:
e74be9ad
213a83ce

Change-Id: If7afc4bb157a6406cabba141d375e9b0dab5f3de
Reviewed-on: https://gerrit.libreoffice.org/41322Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Katarina Behrens <Katarina.Behrens@cib.de>

cui/uiconfig/ui/specialcharacters.ui

@@ -138,7 +138,7 @@
                     <property name="visible">True</property>
                     <property name="can_focus">False</property>
                     <property name="halign">start</property>
-                    <property name="label" translatable="yes">Search:</property>
+                    <property name="label" translatable="yes" context="specialcharacters|srchft">Search:</property>
                   </object>
                   <packing>
                     <property name="left_attach">0</property>

sc/uiconfig/scalc/ui/dataprovider.ui

@@ -162,7 +162,7 @@
                               <object class="GtkLabel" id="label_db">
                                 <property name="visible">True</property>
                                 <property name="can_focus">False</property>
-                                <property name="label" translatable="yes">Database Range:</property>
+                                <property name="label" translatable="yes" context="datastreams|label_db">Database Range:</property>
                               </object>
                               <packing>
                                 <property name="expand">False</property>