Fix problem on linux

doc/makepanda/makepandacore.py

@@ -854,6 +854,7 @@ def SdkLocateVisualStudio():
         SDK["VISUALSTUDIO"] = vcdir
 
 def SdkLocateMSPlatform():
+    if (sys.platform != "win32"): return
     platsdk=GetRegistryKey("SOFTWARE\\Microsoft\\MicrosoftSDK\\InstalledSDKs\\D2FF9F89-8AA2-4373-8A31-C838BF4DBBE1", "Install Dir")
     if (platsdk == 0):
         platsdk=GetRegistryKey("SOFTWARE\\Microsoft\\Microsoft SDKs\\Windows\\v6.1","InstallationFolder")