vlib: use sync.new_mutex() consistently for initialising all vlib structures containing mutex fields

vlib/clipboard/x11/clipboard.c.v

@@ -145,7 +145,7 @@ mut:
 	selection Atom // the selection atom
 	window    Window
 	atoms     []Atom
-	mutex     &sync.Mutex = unsafe { nil }
+	mutex     &sync.Mutex = sync.new_mutex()
 	text      string // text data sent or received
 	got_text  bool   // used to confirm that we have got the text
 	is_owner  bool   // to save selection owner state

vlib/context/cancel.v

@@ -23,10 +23,10 @@ pub struct CancelContext {
 	id string
 mut:
 	context  Context
-	mutex    &sync.Mutex
+	mutex    &sync.Mutex = sync.new_mutex()
 	done     chan int
 	children map[string]Canceler
-	err      IError
+	err      IError = none
 }
 
 // with_cancel returns a copy of parent with a new done channel. The returned

vlib/v/parser/parser.v

@@ -385,8 +385,8 @@ pub fn (mut p Parser) parse() &ast.File {
 struct Queue {
 mut:
 	idx              int
-	mu               &sync.Mutex
-	mu2              &sync.Mutex
+	mu               &sync.Mutex = sync.new_mutex()
+	mu2              &sync.Mutex = sync.new_mutex()
 	paths            []string
 	table            &ast.Table = unsafe { nil }
 	parsed_ast_files []&ast.File

vlib/v/tests/str_gen_test.v

@@ -448,7 +448,7 @@ fn test_fixed_array_of_function() {
 }
 
 struct CTypeDefStruct {
-	mutex &sync.Mutex
+	mutex &sync.Mutex = sync.new_mutex()
 }
 
 fn test_c_struct_typedef() {