installer.sh: fail validation for EFI systems without proper ESP

Right now the installer will print an error dialog but mark the
filesystems done anyway and march on, which will later result
in a failed GRUB installation.

installer.sh.in

@@ -952,6 +952,7 @@ menu_network() {
 validate_filesystems() {
     local mnts dev size fstype mntpt mkfs rootfound fmt
     local usrfound efi_system_partition
+    local bootdev=$(get_option BOOTLOADER)
 
     unset TARGETFS
     mnts=$(grep -E '^MOUNTPOINT.*' $CONF_FILE)
@@ -985,10 +986,11 @@ the mount point for the root filesystem (/) has not yet been configured." ${MSGB
         DIALOG --msgbox "${BOLD}${RED}ERROR:${RESET} \
 /usr mount point has been configured but is not supported, please remove it to continue." ${MSGBOXSIZE}
         return 1
-    elif [ -n "$EFI_SYSTEM" -a -z "$efi_system_partition" ]; then
+    elif [ -n "$EFI_SYSTEM" -a "$bootdev" != "none" -a -z "$efi_system_partition" ]; then
         DIALOG --msgbox "${BOLD}${RED}ERROR:${RESET} \
 The EFI System Partition has not yet been configured, please create it\n
 as FAT32, mountpoint /boot/efi and at least with 100MB of size." ${MSGBOXSIZE}
+        return 1
     fi
     FILESYSTEMS_DONE=1
 }
@@ -1191,17 +1193,10 @@ enable_dhcpd() {
 }
 
 menu_install() {
-    # Don't continue if filesystems are not ready.
-    validate_filesystems || return 1
-
     ROOTPASSWORD_DONE="$(get_option ROOTPASSWORD)"
     BOOTLOADER_DONE="$(get_option BOOTLOADER)"
 
-    if [ -z "$FILESYSTEMS_DONE" ]; then
-        DIALOG --msgbox "${BOLD}Required filesystems were not configured, \
-please do so before starting the installation.${RESET}" ${MSGBOXSIZE}
-        return 1
-    elif [ -z "$ROOTPASSWORD_DONE" ]; then
+    if [ -z "$ROOTPASSWORD_DONE" ]; then
         DIALOG --msgbox "${BOLD}The root password has not been configured, \
 please do so before starting the installation.${RESET}" ${MSGBOXSIZE}
         return 1
@@ -1211,6 +1206,16 @@ configured, please do so before starting the installation.${RESET}" ${MSGBOXSIZE
         return 1
     fi
 
+    # Validate filesystems after making sure bootloader is done,
+    # so that specific checks can be made based on the selection
+    validate_filesystems || return 1
+
+    if [ -z "$FILESYSTEMS_DONE" ]; then
+        DIALOG --msgbox "${BOLD}Required filesystems were not configured, \
+please do so before starting the installation.${RESET}" ${MSGBOXSIZE}
+        return 1
+    fi
+
     DIALOG --yesno "${BOLD}The following operations will be executed:${RESET}\n\n
 ${BOLD}${TARGETFS}${RESET}\n
 ${BOLD}${RED}WARNING: data on partitions will be COMPLETELY DESTROYED for new \