Use JAVA_HOME before bundled jre

Must keep bundled jre symlink around in case "Use Embedded JDK" is selected

https://bugs.gentoo.org/613868
https://bugs.gentoo.org/660404

--- android-studio/bin/studio.sh	2018-07-20 13:43:12.339049033 +0800
+++ android-studio/bin/studio.sh	2018-07-20 13:43:38.494932028 +0800
@@ -73,6 +73,14 @@
   fi
 fi
 
+if [ -z "$JDK" -a -n "$JDK_HOME" -a -x "$JDK_HOME/bin/java" ]; then
+  JDK="$JDK_HOME"
+fi
+
+if [ -z "$JDK" -a  -n "$JAVA_HOME" -a -x "$JAVA_HOME/bin/java" ]; then
+  JDK="$JAVA_HOME"
+fi
+
 if [ -z "$JDK" -a "$OS_TYPE" = "Linux" ] ; then
   BUNDLED_JRE="$IDE_HOME/jre64"
   if [ ! -d "$BUNDLED_JRE" ]; then
@@ -83,14 +91,6 @@
   fi
 fi
 
-if [ -z "$JDK" -a -n "$JDK_HOME" -a -x "$JDK_HOME/bin/java" ]; then
-  JDK="$JDK_HOME"
-fi
-
-if [ -z "$JDK" -a  -n "$JAVA_HOME" -a -x "$JAVA_HOME/bin/java" ]; then
-  JDK="$JAVA_HOME"
-fi
-
 if [ -z "$JDK" ]; then
   JDK_PATH=`which java`