gn format: don't crash when there's no block on a function call

(Child of https://codereview.chromium.org/607173002/)

R=brettw@chromium.org
BUG=348474

Review URL: https://codereview.chromium.org/608593006

Cr-Commit-Position: refs/heads/master@{#297228}

tools/gn/command_format.cc

@@ -242,10 +242,12 @@ Printer::ExprStyle Printer::Expr(const ParseNode* root) {
     Sequence(kSequenceStyleFunctionCall,
              func_call->args()->contents(),
              func_call->args()->End());
-    Print(" ");
-    Sequence(kSequenceStyleBracedBlock,
-             func_call->block()->statements(),
-             func_call->block()->End());
+    if (func_call->block()) {
+      Print(" ");
+      Sequence(kSequenceStyleBracedBlock,
+               func_call->block()->statements(),
+               func_call->block()->End());
+    }
   } else if (const IdentifierNode* identifier = root->AsIdentifier()) {
     Print(identifier->value().value());
   } else if (const ListNode* list = root->AsList()) {

tools/gn/command_format_unittest.cc

@@ -46,3 +46,4 @@ FORMAT_TEST(014)
 FORMAT_TEST(015)
 // TODO(scottmg): Requires precedence/parentheses FORMAT_TEST(016)
 FORMAT_TEST(017)
+FORMAT_TEST(018)

tools/gn/format_test_data/018.gn

+# Don't crash when no block on a function call.
+
+import("wee.gni")

tools/gn/format_test_data/018.golden

+# Don't crash when no block on a function call.
+
+import("wee.gni")