acrobatreaderdc: use mst if present but skip transform if not

packages/acrobatreaderdc.xml

@@ -7,13 +7,30 @@
   <variable name="version" value="20.006.20042" />
   <variable name="mainversion" value="2000620042" />
   <variable name="patchversion" value="2000620042" /> <!-- this may be the same version as mainversion -->
+  <variable name="mstpath" value="%WPKGSHAREBASE%\%WPKGINSTITUTION%-config\Adobe\AcrobatReaderDC\%WPKGINSTITUTION%.mst" />
   <check type="uninstall" condition="versiongreaterorequal" path="Adobe Acrobat Reader DC" value="%version%" />
 
   <!-- patches are cumulative; we only need to apply the latest one -->
-  <install cmd='msiexec /qn /i "%WPKGSOFTWARE%\Adobe\AcrobatReaderDC\%mainversion%\AcroRead.msi" /l* c:\netinst\logs\ReaderDC.log TRANSFORMS="%WPKGSHAREBASE%\%WPKGINSTITUTION%-config\Adobe\AcrobatReaderDC\%WPKGINSTITUTION%.mst"'>
+  <!-- use mst as a TRANSFORM(s) if present.... -->
+  <install cmd='msiexec /qn /i "%WPKGSOFTWARE%\Adobe\AcrobatReaderDC\%mainversion%\AcroRead.msi" /l* c:\netinst\logs\ReaderDC.log TRANSFORMS="%mstpath%"'>
     <exit code="0" />
     <exit code="3010" reboot="false" />
+    <condition>
+      <check type="file" condition="exists" path="%mstpath%" />
+    </condition>
   </install>
+
+  <!-- ...but no TRANSFORMS if we don't have the mst -->
+  <install cmd='msiexec /qn /i "%WPKGSOFTWARE%\Adobe\AcrobatReaderDC\%mainversion%\AcroRead.msi" /l* c:\netinst\logs\ReaderDC.log '>
+    <exit code="0" />
+    <exit code="3010" reboot="false" />
+    <condition>
+      <check type="logical" condition="not">
+        <check type="file" condition="exists" path="%mstpath%" />
+      </check>
+    </condition>
+  </install>
+
   <install cmd='msiexec /qn /l* %WPKGLOGDIR%\ReaderDC-p1.log /update "%WPKGSOFTWARE%\Adobe\AcrobatReaderDC\AcroRdrDCUpd%patchversion%.msp"'>
     <exit code="3010" reboot="false" />
   </install>