[clang-format] Fix an assertion failure on -lines=0:n

[owenpan]

Summary

Also fixed the error message for start line > end line and added test cases.

Fixes https://github.com/llvm/llvm-project/issues/56438.

[curdeius]

👍

clang/test/Format/line-ranges.cpp

 // RUN: grep -Ev "// *[A-Z-]+:" %s \
 // RUN:   | clang-format -style=LLVM -lines=1:1 -lines=5:5 \
 // RUN:   | FileCheck -strict-whitespace %s
 // CHECK: {{^int\ \*i;$}}
   int*i;
 
 // CHECK: {{^int\ \ \*\ \ i;$}}
 int  *  i; 
 
 // CHECK: {{^int\ \*i;$}}
 int   *   i;
+
+// RUN: not clang-format -lines=0:1 < %s 2>&1 \
+// RUN:   | FileCheck -strict-whitespace -check-prefix=CHECK0 %s
+// CHECK0: error: start line should be at least 1
+
+// RUN: not clang-format -lines=2:1 < %s 2>&1 \
+// RUN:   | FileCheck -strict-whitespace -check-prefix=CHECK1 %s
+// CHECK1: error: start line should not exceed end line

clang/tools/clang-format/ClangFormat.cpp

if (!LineRanges.empty()) {
     }
 
     for (unsigned i = 0, e = LineRanges.size(); i < e; ++i) {
       unsigned FromLine, ToLine;
       if (parseLineRange(LineRanges[i], FromLine, ToLine)) {
         errs() << "error: invalid <start line>:<end line> pair\n";
         return true;
       }
+      if (FromLine < 1) {
+        errs() << "error: start line should be at least 1\n";
+        return true;
+      }
       if (FromLine > ToLine) {
-        errs() << "error: start line should be less than end line\n";
+        errs() << "error: start line should not exceed end line\n";
         return true;
       }
       SourceLocation Start = Sources.translateLineCol(ID, FromLine, 1);
       SourceLocation End = Sources.translateLineCol(ID, ToLine, UINT_MAX);
       if (Start.isInvalid() || End.isInvalid())
         return true;
       unsigned Offset = Sources.getFileOffset(Start);
       unsigned Length = Sources.getFileOffset(End) - Offset;