Guard MOZ_GMP_PATH for multiple inclusion

Otherwise we get the same path repeated once for every subshell that
sources the profile.d scripts.

openh264.spec

@@ -136,8 +136,10 @@ EOF
 
 mkdir -p $RPM_BUILD_ROOT%{_sysconfdir}/profile.d
 cat > $RPM_BUILD_ROOT%{_sysconfdir}/profile.d/gmpopenh264.sh << 'EOF'
-MOZ_GMP_PATH="${MOZ_GMP_PATH}${MOZ_GMP_PATH:+:}%{_libdir}/mozilla/plugins/gmp-gmpopenh264/system-installed"
+if [[ ":$MOZ_GMP_PATH:" != *":%{_libdir}/mozilla/plugins/gmp-gmpopenh264/system-installed:"* ]]; then
-export MOZ_GMP_PATH
+    MOZ_GMP_PATH="${MOZ_GMP_PATH}${MOZ_GMP_PATH:+:}%{_libdir}/mozilla/plugins/gmp-gmpopenh264/system-installed"
+    export MOZ_GMP_PATH
+fi
 EOF
 
 mkdir -p $RPM_BUILD_ROOT%{_datadir}/fish/vendor_conf.d