Only check for Go version if a compiler was found.

This fixes a syntax error in the code which would occur when no Go compiler was found at all.

git-svn-id: https://swig.svn.sourceforge.net/svnroot/swig/trunk@12333 626c5289-ae23-0410-ae9c-e8d60b6d4f22

configure.in

@@ -2006,6 +2006,7 @@ else
 	GO="$GOBIN"
     fi
 
+    if test -n "$GO" ; then
       GOGCC=false
       if $GO --help 2>/dev/null | grep gccgo >/dev/null 2>&1 ; then
   	GOGCC=true
@@ -2016,7 +2017,7 @@ else
   	    GO=
   	fi
       fi
-
+    fi
 fi
 
 AC_SUBST(GOGCC)