Fix reading environment variables with newline

Summary:
Use '\0' as separator as '\n' is likely to appear in values.

BUG: 413130

Test Plan:
/etc/profile.d/mc.sh exported an mc() function,
which resulted in "syntax error: unexpected end of file" in the Plasma session.
Now the mc function is correctly set in the environment.

Reviewers: #plasma, apol, davidedmundson, adridg

Reviewed By: #plasma, apol, davidedmundson, adridg

Subscribers: davidedmundson, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D24750

startkde/plasma-sourceenv.sh

@@ -3,4 +3,4 @@ do
     . $i >/dev/null
 done
 
-env
+env -0

startkde/startplasma.cpp

@@ -91,7 +91,7 @@ void sourceFiles(const QStringList &files)
     p.waitForFinished(-1);
 
     const auto fullEnv = p.readAllStandardOutput();
-    auto envs = fullEnv.split('\n');
+    auto envs = fullEnv.split('\0');
 
     for (auto &env: envs) {
         if (env.startsWith("_=") || env.startsWith("SHLVL"))