Fix crash in CheckUninitVar (#2129)

http://cppcheck.osuosl.org:8000/ycmd
```
2019-08-30 23:21
ftp://ftp.se.debian.org/debian/pool/main/y/ycmd/ycmd_0+20181101+git600f54d.orig.tar.gz
cppcheck-options: -j1 --library=posix --library=gnu --library=qt --library=python --library=googletest --library=boost -D__GNUC__ --check-library --inconclusive --enable=style,information --platform=unix64 --template=daca2 -rp=temp temp
platform: Linux-4.15.0-58-generic-x86_64-with-Ubuntu-18.04-bionic
python: 2.7.15+
client-version: 1.1.31
cppcheck: head 1.88
count: Crash! 83
elapsed-time: -11.0 61.2
head results:
Checking temp/ycmd-0+20181101+git600f54d/ycmd/tests/clang/testdata/completion_fixit.cc: __GNUC__=1...

Program received signal SIGSEGV, Segmentation fault.
CheckUninitVar::valueFlowUninit (this=this@entry=0x7fffffffb350) at build/checkuninitvar.cpp:2376
2376	            if (!tok->variable())
 #0  CheckUninitVar::valueFlowUninit (this=this@entry=0x7fffffffb350) at build/checkuninitvar.cpp:2376
 #1  0x00005555556901ac in CheckUninitVar::runChecks (this=<optimized out>, tokenizer=0x7fffffffbcb0, settings=0x7fffffffcd10, errorLogger=<optimized out>) at lib/checkuninitvar.h:68
 #2  0x00005555556a2210 in CppCheck::checkNormalTokens (this=this@entry=0x7fffffffcaf0, tokenizer=...) at build/cppcheck.cpp:730
 #3  0x00005555556a6ee2 in CppCheck::checkFile (this=this@entry=0x7fffffffcaf0, filename="temp/ycmd-0+20181101+git600f54d/ycmd/tests/clang/testdata/completion_fixit.cc", cfgname="", fileStream=...) at build/cppcheck.cpp:540
 #4  0x00005555556aad4c in CppCheck::check (this=this@entry=0x7fffffffcaf0, path="temp/ycmd-0+20181101+git600f54d/ycmd/tests/clang/testdata/completion_fixit.cc") at build/cppcheck.cpp:195
 #5  0x00005555557ef167 in CppCheckExecutor::check_internal (this=this@entry=0x7fffffffd880, cppcheck=..., argv=argv@entry=0x7fffffffdc08) at cli/cppcheckexecutor.cpp:884
 #6  0x00005555557efa9a in CppCheckExecutor::check (this=0x7fffffffd880, argc=17, argv=0x7fffffffdc08) at cli/cppcheckexecutor.cpp:198
 #7  0x00005555555b1d1b in main (argc=17, argv=0x7fffffffdc08) at cli/main.cpp:95
```

lib/checkuninitvar.cpp

@@ -1333,7 +1333,7 @@ void CheckUninitVar::valueFlowUninit()
     for (const Scope &scope : symbolDatabase->scopeList) {
         if (!scope.isExecutable())
             continue;
-        for (const Token* tok = scope.bodyStart; tok != scope.bodyEnd; tok = tok->next()) {
+        for (const Token* tok = scope.bodyStart; tok && tok != scope.bodyEnd; tok = tok->next()) {
             if (Token::simpleMatch(tok, "sizeof (")) {
                 tok = tok->linkAt(1);
                 continue;

test/testuninitvar.cpp

@@ -83,6 +83,7 @@ class TestUninitVar : public TestFixture {
         TEST_CASE(valueFlowUninit);
         TEST_CASE(uninitvar_ipa);
         TEST_CASE(uninitvar_memberfunction);
+        TEST_CASE(uninitvar_nonmember); // crash in ycmd test
 
         TEST_CASE(isVariableUsageDeref); // *p
 
@@ -4441,6 +4442,18 @@ class TestUninitVar : public TestFixture {
         ASSERT_EQUALS("[test.cpp:6]: (error) Uninitialized variable: c\n", errout.str());
     }
 
+    void uninitvar_nonmember() {
+        valueFlowUninit( "struct Foo {\n"
+                         "  int bar;\n"
+                         "};\n"
+                         "\n"
+                         "int main() {\n"
+                         "  Foo* foo;\n"
+                         "  foo.b\n"
+                         "}\n");
+        ASSERT_EQUALS("[test.cpp:7]: (error) Uninitialized variable: foo\n", errout.str());
+    }
+
     void isVariableUsageDeref() {
         // *p
         checkUninitVar("void f() {\n"