Resolves: rhbz#1092589 Thoroughly check whether JRE is still present

...not only on Mac OS X.  Was able to reproduce this on Fedora 20 where current
JRE was /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.5.x86_64 but for whatever reason
there was also a left-behind /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.0.x86_64 tree
(containing just a handful of sub-dirs, but no real content) that was still
recorded in my ~/.config/libreoffice/4/user/config/javasettings_Linux_X86_64.xml

Change-Id: Ie477c5a506a430f6c29525f6c558dbc18bbf1c48

jvmfwk/plugins/sunmajor/pluginlib/sunjavaplugin.cxx

@@ -772,10 +772,10 @@ javaPluginError jfw_plugin_existJRE(const JavaInfo *pInfo, sal_Bool *exist)
     {
         ret = JFW_PLUGIN_E_ERROR;
     }
-#ifdef MACOSX
     //We can have the situation that the JavaVM runtime library is not
     //contained within JAVA_HOME. Then the check for JAVA_HOME would return
     //true although the runtime library may not be loadable.
+    //Or the JAVA_HOME directory of a deinstalled JRE left behind.
     if (ret == JFW_PLUGIN_E_NONE && *exist == sal_True)
     {
         OUString sRuntimeLib = getRuntimeLib(pInfo->arVendorData);
@@ -803,7 +803,6 @@ javaPluginError jfw_plugin_existJRE(const JavaInfo *pInfo, sal_Bool *exist)
                        + sRuntimeLib + " \n");
         }
     }
-#endif
     return ret;
 }