-j 0 causes indefinite hang. require >= 1 (#5326)

In cppcheck 2.11.1 (macOS), using `-j 0` actually causes cppcheck to do
nothing–it stalls indefinitely.

I could only find one place where `mSettings.jobs` was validated against
> 0 and it's simply an assert, so you wouldn't hit it in a release
build.

- Require -j >= 1 ✅
- Cap -j at 1024, not 10000 ✅ (I don't even know what would happen if
you created 10,000 threads, but nothing good; likely exhaust virtual
memory or grind the process to a halt). 1024 is still obscene but there
may be some hypercomputers out there that have that many logical cores.

cli/cmdlineparser.cpp

@@ -507,10 +507,17 @@ bool CmdLineParser::parseFromArgs(int argc, const char* const argv[])
                     printError("argument to '-j' is not valid - " +  err + ".");
                     return false;
                 }
-                if (tmp > 10000) {
+                if (tmp == 0) {
-                    // This limit is here just to catch typos. If someone has
+                    // TODO: implement get CPU logical core count and use that.
-                    // need for more jobs, this value should be increased.
+                    // Usually, -j 0 would mean "use all available cores," but
-                    printError("argument for '-j' is allowed to be 10000 at max.");
+                    // if we get a 0, we just stall and don't do any work.
+                    printError("argument for '-j' must be greater than 0.");
+                    return false;
+                }
+                if (tmp > 1024) {
+                    // Almost nobody has 1024 logical cores, but somebody out
+                    // there does.
+                    printError("argument for '-j' is allowed to be 1024 at max.");
                     return false;
                 }
                 mSettings.jobs = tmp;

test/testcmdlineparser.cpp

@@ -142,6 +142,7 @@ private:
         TEST_CASE(jobs2);
         TEST_CASE(jobsMissingCount);
         TEST_CASE(jobsInvalid);
+        TEST_CASE(jobsNoJobs);
         TEST_CASE(jobsTooBig);
         TEST_CASE(maxConfigs);
         TEST_CASE(maxConfigsMissingCount);
@@ -1010,11 +1011,18 @@ private:
         ASSERT_EQUALS("cppcheck: error: argument to '-j' is not valid - not an integer.\n", GET_REDIRECT_OUTPUT);
     }
 
+    void jobsNoJobs() {
+        REDIRECT;
+        const char * const argv[] = {"cppcheck", "-j0", "file.cpp"};
+        ASSERT(!parser->parseFromArgs(3, argv));
+        ASSERT_EQUALS("cppcheck: error: argument for '-j' must be greater than 0.\n", GET_REDIRECT_OUTPUT);
+    }
+
     void jobsTooBig() {
         REDIRECT;
-        const char * const argv[] = {"cppcheck", "-j10001", "file.cpp"};
+        const char * const argv[] = {"cppcheck", "-j1025", "file.cpp"};
         ASSERT(!parser->parseFromArgs(3, argv));
-        ASSERT_EQUALS("cppcheck: error: argument for '-j' is allowed to be 10000 at max.\n", GET_REDIRECT_OUTPUT);
+        ASSERT_EQUALS("cppcheck: error: argument for '-j' is allowed to be 1024 at max.\n", GET_REDIRECT_OUTPUT);
     }
 
     void maxConfigs() {