cmGlobalGenerator: Fix CheckTargetsForMissingSources after refactoring

Refactoring in commit 01b2d6ab74 (Modernize: Use ranged for-loops when
possible, 2019-02-07, v3.15.0-rc1~575^2) accidentally changed a loop
condition in this method from "keep iterating if srcs.empty()" to
"stop iterating if srcs.empty()".  Switch it back.

The bug could only manifest in very subtle conditions in a multi-config
generator.  Add one such case to the test suite.

Fixes: #20706

1 files changed, 1 insertions, 1 deletions

diff --git a/Source/cmGlobalGenerator.cxx b/Source/cmGlobalGenerator.cxx
index 6370ed2..cfad4c2 100644
--- a/Source/cmGlobalGenerator.cxx
+++ b/Source/cmGlobalGenerator.cxx
@@ -320,7 +320,7 @@ bool cmGlobalGenerator::CheckTargetsForMissingSources() const
       } else {
         for (std::string const& config : configs) {
           target->GetSourceFiles(srcs, config);
-          if (srcs.empty()) {
+          if (!srcs.empty()) {
             break;
           }
         }