Fix post/windows/gather/credentials/steam for an empty env var

Author: wchen-r7

modules/post/windows/gather/credentials/steam.rb

@@ -42,7 +42,7 @@ def run
     # We will just use an x64 only defined env variable to check.
     progfiles_env = session.sys.config.getenvs('ProgramFiles(X86)', 'ProgramFiles')
     progfilesx86 = progfiles_env['ProgramFiles(X86)']
-    if not progfilesx86.empty? and progfilesx86 !~ /%ProgramFiles\(X86\)%/
+    if not progfilesx86.blank? and progfilesx86 !~ /%ProgramFiles\(X86\)%/
       progs = progfilesx86 # x64
     else
       progs = progfiles_env['ProgramFiles'] # x86