plugins/java: quote path && `shfmt`

Provides an error message if no file is specified.

clean_files.txt

@@ -97,6 +97,7 @@ plugins/available/history-search.plugin.bash
 plugins/available/history-substring-search.plugin.bash
 plugins/available/history.plugin.bash
 plugins/available/hub.plugin.bash
+plugins/available/java.plugin.bash
 plugins/available/jump.plugin.bash
 plugins/available/less-pretty-cat.plugin.bash
 plugins/available/node.plugin.bash

plugins/available/java.plugin.bash

@@ -1,4 +1,4 @@
-cite about-plugin
+# shellcheck shell=bash
 about-plugin 'Java and JAR helper functions'
 
 function jar_manifest {
@@ -7,5 +7,5 @@ function jar_manifest {
 	param '1: JAR file to extract the MANIFEST from'
 	example 'jar_manifest lib/foo.jar'
 
-  unzip -c $1 META-INF/MANIFEST.MF
+	unzip -c "${1?${FUNCNAME[0]}: JAR file must be specified}" META-INF/MANIFEST.MF
 }