Fix PROPERTY line regex

Fixes orgzly/orgzly-android#726.

Author: nevenz

src/main/java/com/orgzly/org/OrgPatterns.java

@@ -41,7 +41,8 @@ public class OrgPatterns {
     public static final Pattern HEAD_PRIORITY_P = Pattern.compile("^\\s*\\[#([A-Z])](.*)");
     public static final Pattern HEAD_TAGS_P = Pattern.compile("^(.*)\\s+:(\\S+):\\s*$");
 
-    public static final Pattern PROPERTY = Pattern.compile("^:([^:\\s]+):(\\s+.+|)$");
+    // org-property-re
+    public static final Pattern PROPERTY = Pattern.compile("^[ \\t]*:(\\S+):(|[ \\t]+.*?[ \\t]*)$");
 
     /*
     https://orgmode.org/manual/In_002dbuffer-settings.html

src/test/java/com/orgzly/org/OrgPropertiesTest.java

@@ -169,4 +169,22 @@ public void compositeWithBreak() throws IOException {
         Assert.assertEquals(4, head.getProperties().size());
         Assert.assertEquals("c d", head.getProperties().get("KEY"));
     }
+
+    @Test
+    public void headerArguments() throws IOException {
+        String fileContent =
+                "* Test heading\n" +
+                        ":PROPERTIES:\n" +
+                        ":header-args: :cache yes\n" +
+                        ":header-args:python:: :results output\n" +
+                        ":END:";
+
+        OrgParsedFile file = parserBuilder.setInput(fileContent).build().parse();
+        OrgHead head = file.getHeadsInList().get(0).getHead();
+
+        Assert.assertTrue(head.hasProperties());
+        Assert.assertEquals(2, head.getProperties().size());
+        Assert.assertEquals(":cache yes", head.getProperties().get("header-args"));
+        Assert.assertEquals(":results output", head.getProperties().get("header-args:python:"));
+    }
 }