Windows: Warn user about needed hotfix

BUG: 394905
FIXED-IN: 3.0.2

windows/installer.nsi

@@ -402,6 +402,7 @@ Function .onInit
         doAbort:
             Abort
     skip:
+        call notifyUserIfHotfixNeeded
 FunctionEnd
 
 Function RegisterCapabilities
@@ -491,3 +492,20 @@ Function SkipComponentsIfPortableInstalltion
 StrCmp $installAsPortable "YES" 0 +2
     Abort
 FunctionEnd
+
+Function notifyUserIfHotfixNeeded
+    ; check if Windows 10 family. Taken from: http://nsis.sourceforge.net/Get_Windows_version
+    ReadRegStr $R0 HKLM "SOFTWARE\Microsoft\Windows NT\CurrentVersion" CurrentMajorVersionNumber
+    StrCmp $R0 '' 0 skiphotfixwarn
+
+    ClearErrors
+    nsExec::ExecToStack 'cmd /Q /C "%SYSTEMROOT%\System32\wbem\wmic.exe qfe get hotfixid | %SYSTEMROOT%\System32\findstr.exe "^KB2999226""'
+    Pop $0 ; return value (it always 0 even if an error occured)
+    Pop $1 ; command output KB2999226
+
+    StrCmp $1 "" 0 skiphotfixwarn
+      MessageBox MB_YESNO|MB_ICONQUESTION "${MSG_HotfixNeeded}" IDNO +2
+        ExecShell open "https://support.microsoft.com/en-us/help/2999226/update-for-universal-c-runtime-in-windows"
+
+    skiphotfixwarn:
+FunctionEnd

windows/strings.nsh

@@ -37,3 +37,5 @@
 !define MSG_InvalidInstallPath "Install path invalid!"
 
 !define MSG_PortableWriteError "Error occurred when creating 'falkon.conf' in installation folder. Create it manually."
+
+!define MSG_HotfixNeeded "To run Falkon you have to install hotfix 'KB2999226'. Proceed to Windows update website?"