Fix Coverity reports of uninitialized scalar variable

Fixes most current reports on Coverity Scan of uninitialized scalar
variable (CWE-457): https://cwe.mitre.org/data/definitions/457.html

These happen most of the time (in our code) when instanciating structs
without a constructor (or with an incomplete one), and later returning
the instance. This is sometimes intended though, as some parameters are
only used in some situations and should not be double-initialized for
performance reasons (e.g. `constant` in ShaderLanguage::Token).

platform/uwp/export/export.cpp

@@ -122,6 +122,14 @@ class AppxPackager {
 		Vector<BlockHash> hashes;
 		uLong file_crc32;
 		ZPOS64_T zip_offset;
+
+		FileMeta() :
+				lfh_size(0),
+				compressed(false),
+				compressed_size(0),
+				uncompressed_size(0),
+				file_crc32(0),
+				zip_offset(0) {}
 	};
 
 	String progress_task;