Enable Uwe to move between installer download screens and still preserve his chosen path.

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/branches/BRANCH_1_3_X@10042 a592a061-630c-0410-9148-cb99ea01b6c8

development/Win32/packaging/installer/download.nsh

@@ -136,8 +136,9 @@
 !macro DownloadEnter_Private ExePath RegistryKey RegistrySubKey RemoveFromPath AddtoPath Required DownloadLabel HomeLabel PageHeader PageDescription
  !define skipBackupLbl "skipBackup_${__LINE__}"
 
-  StrCpy ${ExePath} ""
-  ReadRegStr ${ExePath} HKLM "${RegistryKey}" "${RegistrySubKey}"
+  ${if} ${ExePath} == ""
+    ReadRegStr ${ExePath} HKLM "${RegistryKey}" "${RegistrySubKey}"
+  ${endif}
 
   !insertmacro MUI_INSTALLOPTIONS_WRITE "ioDownload.ini" "Field 1" "Text" ""
   !insertmacro MUI_INSTALLOPTIONS_WRITE "ioDownload.ini" "Field 2" "Text" "$(DownloadPageField2)"

development/Win32/packaging/installer/lyx_installer.nsi

@@ -306,13 +306,19 @@ Function .onInit
     !undef READ_ONLY
   ${endif}
 
+  StrCpy $MinSYSPath ""
+  StrCpy $PythonPath ""
+  StrCpy $MiKTeXPath ""
+  StrCpy $PerlPath ""
+  StrCpy $GhostscriptPath ""
+  StrCpy $ImageMagickPath ""
+
   ClearErrors
 FunctionEnd
 
 ;--------------------------------
 
 Function DownloadMinSYS
-  StrCpy $MinSYSPath ""
   StrCpy $DownloadMinSYS "0"
 
   ; Search the registry for the MinSYS uninstaller.
@@ -361,7 +367,6 @@ FunctionEnd
 ;--------------------------------
 
 Function DownloadPython
-  StrCpy $PythonPath ""
   StrCpy $DownloadPython "0"
 
   ${DownloadEnter} \
@@ -389,7 +394,6 @@ FunctionEnd
 
 Function DownloadMiKTeX
   StrCpy $DoNotRequireMiKTeX "1"
-  StrCpy $MiKTeXPath ""
   StrCpy $DownloadMiKTeX "0"
 
   ${DownloadEnter} \
@@ -417,7 +421,6 @@ FunctionEnd
 
 Function DownloadPerl
   StrCpy $DoNotRequirePerl "1"
-  StrCpy $PerlPath ""
   StrCpy $DownloadPerl "1"
 
   ${DownloadEnter} \
@@ -445,7 +448,6 @@ FunctionEnd
 
 Function DownloadGhostscript
   StrCpy $DoNotRequireGhostscript "1"
-  StrCpy $GhostscriptPath ""
   StrCpy $DownloadGhostscript "0"
 
   ; Find which version of ghostscript, if any, is installed.
@@ -481,7 +483,6 @@ FunctionEnd
 
 Function DownloadImageMagick
   StrCpy $DoNotRequireImageMagick "1"
-  StrCpy $ImageMagickPath ""
   StrCpy $DownloadImageMagick "0"
 
   ${DownloadEnter} \