[geary] Fix a shell warning running configure under flatpak-builder.

[Michael Gratton <mjog src gnome org>]

commit 4cab543e1b2ba1a69b669ccebc3ecf7a053c5cad
Author: Michael James Gratton <mike vee net>
Date:   Mon Feb 27 21:34:36 2017 +1100

    Fix a shell warning running configure under flatpak-builder.

 configure |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/configure b/configure
index bf47117..86a029f 100755
--- a/configure
+++ b/configure
@@ -73,7 +73,7 @@ do
                             exit 0
                             ;;
 
-        --prefix)           if [ -z "$value"]; then
+        --prefix)           if [ -z "$value" ]; then
                                 # handle jhbuild's use of "--prefix /path"
                                 value="$2"
                                 shift
@@ -85,7 +85,7 @@ do
         # ignored for autotools compatibility
         --bindir | --libdir | --sbindir | --datadir | --localstatedir | \
         --includedir | --infodir | --sysconfdir |  --mandir | --libexecdir)
-                            if [ -z "$value"]; then
+                            if [ -z "$value" ]; then
                                 # handle jhbuild's use of "--option /path"
                                 value="$2"
                                 shift