[wue] fix MSA bypass not being applied unless SB/TPM or RAM/Disk bypass is also selected

* In a manner that defies logic, Microsoft designed Windows setup to parse Autounattend.xml
  for windowsPE tasks in the PE environment, but only carry out the copying of that file
  to %WINDIR%\Panther for subsequent processing with the other passes *IF* there exist an
  actual windowsPE section.
* In short, when using the Autounattend.xml method, Microsoft have made all passes there
  dependent on the existence of a windowsPE pass, regardless of whether that pass has any
  use or not.
* Working around this would be fine and all (just add an empty windowsPE pass so that the
  later passes get executed) if the absence of a windowsPE pass didn't also determine
  whether the user will be presented with the default Windows setup screens that include
  the "Repair your computer" option or a completely different set of screens (c.f. #1971).
* This means that, to keep users happy, we need to add yet another method to carry out
  tasks that should have remained the realm of boot.wim's Autounattend.xml, and instead
  create a \sources\$OEM$\$$\Panther\unattend.xml when there are no windowsPE tasks (on
  account that setup copies anything found under \sources\$OEM$\$$\ to %WINDIR%\).
  Only through this can we have the specialize and oobeSystem tasks actually carried out
  (for bypassing MSA requirements of skipping the data collection screens) while keeping
  the original Windows Setup look and feel.
* Closes #1981

src/rufus.c

@@ -1283,7 +1283,7 @@ static char* CreateUnattendXml(int arch, int mask)
 		// WinPE will complain if we don't provide a product key. *Any* product key. This is soooo idiotic...
 		fprintf(fd, "      <UserData>\n");
 		fprintf(fd, "        <ProductKey>\n");
-		fprintf(fd, "          <Key>xxxxx-xxxxx-xxxxx-xxxxx-xxxxx</Key>\n");
+		fprintf(fd, "          <Key />\n");
 		fprintf(fd, "        </ProductKey>\n");
 		fprintf(fd, "      </UserData>\n");
 		fprintf(fd, "      <RunSynchronous>\n");